The title logo appears on a black background. The scene opens in Dr. Emmett Brown's (Christopher Lloyd) garage/home laboratory as the camera pan over a large collection of clocks. A robotic tin can opener opens a tin of spoiled dog food and empties the contents into an overflowing dog food bowl marked "Einstein". The television set and radio turn on. On the TV, we see the ending of an advertisement, followed by a woman newscaster announcing the recent theft of a case of plutonium.
The front door of the garage opens, and Marty McFly (Michael J. Fox) comes in. Marty calls out, then reaches down to partly lift up the doormat. He places a set of keys under the doormat, then drops it back down. Marty enters the garage, calling out for Doc and whistling for Einstein. He comments on the mess the place is in.
Marty puts down his skateboard and it rolls along the floor until it hits a hidden box of plutonium. He turns on Doc's amplifier system, turning all the settings to maximum. A hum grows louder in the background. Marty plugs his electric guitar into a huge amplifier, pauses, and then plucks a string. The amplifier blows up, the impact throwing Marty back against a bookshelf, which falls, causing the books and papers on it to fall off and land on his head. Marty lifts up his sunglasses and we finally get to see his face.
"Whoa... rock and roll," he says, when a loud ringing fills the garage. It sounds like a fire alarm, but then turns out to be just the telephone. Marty scrambles off the ground and answers it. It's Doc, who asks Marty to meet him that night at the Twin Pines Mall at 1:15 a.m. Marty asks him where he's been all week. Doc says that he has been working. Marty tells him that his equipment had been left on all week. Remembering, Doc tells Marty not to hook up to the amplifier. "There's a slight possibility of overload," he says. Marty glances at the destroyed amplifier, and says that he'll keep that in mind.
Just then, every single one of the numerous clocks go off at once, chiming loudly, and Doc asks about them. Marty tells him that it's eight o'clock. Doc is elated at the information, as it means that his experiment has worked and all his clocks are 25 minutes slow....meaning it really is 8:25, and Marty is late for school. He exclaims this news into the telephone, slams down the receiver, retrieves his skateboard and rushes out of the garage. Marty gets on his skateboard and skates through the streets, hitching a ride first on a pickup truck and then on another Jeep to get through town.
Marty arrives outside Hill Valley High School. He hops off his skateboard and flips it up into his hand. His girlfriend Jennifer Parker (Claudia Wells) is waiting for him. She warns him that the principal, Mr. Strickland (James Tolkan) is looking for him. Marty tells her that his lateness is not his fault, because Doc set his clocks slow. Strickland suddenly appears at the sound of Doc's name. He demands to know if Marty is still hanging around with Doc, and hands him and Jennifer a tardy slip each; it is Marty's fourth in a row. Strickland warns Marty that Doc is a dangerous nutcase, and if he continues hanging out with him, he'll get in trouble. Strickland also harshly tells Marty that he is a slacker, just like his father. "No McFly ever amounted to anything in the history of Hill Valley!" he says, bringing his face closer to Marty's until their noses touch. Marty counters that history will be changing soon.
We change to the auditorium, where a band has just finished playing. Four judges sit on chairs before the stage and request the next band. Marty and his band get up on stage and he introduces them as The Pinheads before launching into the opening bars of a ramped up, Heavy Metal Version of "The Power of Love". One of the judges (the song's artist, Huey Lewis, in a cameo appearance) cuts them off and tells them that they are too loud.
After school, Marty and Jennifer are walking through the Courthouse Square as a mayoral campaign van drives past, blaring "Re-elect Mayor Goldie Wilson!" over its loudspeakers. Marty tells Jennifer about how he doubts he'll ever get anywhere with his music. Jennifer tries to reassure him with her opinion that he's really good, and encourages him to send in his audition tape to the record company, but Marty expresses fear that they'll reject him. He looks up as a new 4x4 Toyota pickup truck is delivered to the Statler Toyota dealership across the street, and admires it, musing about taking Jennifer in it for a weekend trip to the lake. Jennifer asks if Marty's mother knows about their plans for the next night. Marty assures her that his mother thinks he's going camping with the guys, and that she would freak out if she knew the truth. Marty fears his mother was probably born a nun. Jennifer assures him that she's just trying to keep him respectable. Their lips come closer, but just as they are about to kiss, a tin can is shoved in their faces by a woman shouting "Save the clock tower! Save the clock tower!" The woman asks them to deposit money that will be contributed to a fund to save the clock tower, which has been frozen at 10:04 ever since it was struck by lightning at that exact time on the night of November 12, 1955. The mayor would like the clock to be replaced, the Hill Valley Preservation Society thinks that it is important part of their heritage and should be left alone. Marty gives her a quarter just to get her to go away. She thanks him and hands him a flyer, before going off to target more unsuspecting passersby.
Marty and Jennifer, now rid of the collection lady, are about to kiss when a car pulls up and beeps its horn loudly. It's Jennifer's father, coming to pick her up. Jennifer hastily scribbles her number on the back of the clock tower flyer with "Love You!!!" next to that. She gets into the car. Marty looks at the back of the flyer. He smiles.
Marty gets back on his skateboard and grabs a police car to tail behind. He makes his way back to his home neighborhood, Lyon Estates. Marty lets go of another car and skims down this opening towards his house.
As Marty rides up to his house, he passes a wrecked BMW sedan being pushed back into the driveway by a tow truck. Inside, Marty's father George McFly (Crispin Glover) is arguing with his supervisor Biff Tannen (Thomas F. Wilson). Biff is exasperated that George loaned him a car without warning him that it had a blind spot, leading him to have a head-on collision with another vehicle. George insists that he never knew the car had a blind spot. He sees Marty and gives him a weak greeting, as Biff demands to know who is going to pay for his cleaning bill, seeing as he spilled beer all over his coattails. Biff then asks George if he's finished filling out Biff's reports. When George admits he hasn't done them yet, an annoyed Biff taps him several times on the head, reminding George that he needs time to retype them because he'll be fired if he hands in his reports in George's handwriting. He expresses despair that all they've got in the fridge is "light" beer, and helps himself to a beer before leaving. After Biff leaves, George hesitantly admits to Marty that he isn't good at confrontations. Marty asks about the car, which he had been planning to drive up to the lake with Jennifer. George apologizes.
The whole of the McFly family later sits down to dinner - George, his wife Lorraine (Lea Thompson), and their children Marty, Dave (Marc McClure) and Linda (Wendie Jo Sperber). Lorraine drops a thin cake onto the table. It says 'Welcome Home, Joey', next to a picture of a bird flying out of jail. Uncle 'Jailbird' Joey has failed to make parole, again. Linda chides that he's an embarrassment to the family. Lorraine reminds her that everyone makes mistakes in life. During dinner, while watching an episode of the Honeymooners on TV, Georgo begins laughing at it, a very weird, nerdy laugh, while the rest of the family stares at him
Having enough of the conversation, Dave leaves for his job as a Burger King cashier, while Linda tells Marty that Jennifer called asking for him. This upsets Lorraine, who lectures Marty that 'any girl who calls a boy is just asking for trouble.' When Linda tries to defend Marty, Lorraine grows upset, insisting that when she was Linda's age she never 'chased a boy, or called a boy, or sat in a parked car with a boy.' Linda asks how she's supposed to meet anyone if she is to go through life like Lorraine did. Lorraine explains that it will happen just like she met George. Linda rolls her eyes, as Lorraine once again relates the story of how they met: supposedly, George was up in a tree (just what he was doing, George has never explained), when he slipped, fell into the street and was hit by Lorraine's father's car. After taking him inside, and taking care of him, Lorraine felt sorry enough for George that she asked him to the Enchantment Under The Sea Dance, which happened to be the same night the lightning bolt struck the clock tower. When they had their first kiss at the dance, she knew she was going to spend the rest of her life with him. George starts once again with his weird, nerdy laugh at the TV while the family just stares at him in disbelief.
Sometime after midnight, Marty is awoken by a call from Doc, who asks Marty to stop by the lab and pick up his video camera that he forgot. Marty does so, and heads to the Twin Pines Mall. When he gets there, he finds Doc's van sitting in the parking lot, with his dog, Einstein, sitting nearby. When Marty goes down to greet Einstein, the rear of the van opens up, and a heavily modified DeLorean DMC-12 sedan is backed down the ramp. The driver's door lifts up, and Doc emerges from the vehicle, greeting Marty, then instructs Marty to start recording.
Doc places Einstein in the DeLorean and buckles him in, having Marty note the exact time on the watch around Einstein's collar, and in Doc's hand. Both are synchronized to the same time. Doc then closes the DeLorean's door, and pulls out a remote control, that he uses to maneuver the DeLorean around the parking lot. When the vehicle is a specific distance away, Doc puts its brakes on, and starts ramping up its speed, before turning off the brakes, sending the DeLorean streaking right towards him and Marty. Suddenly, a bright light is seen from inside the DeLorean, as additional fire and lights are set off around it, and suddenly, upon hitting 88 miles per hour, the car vanishes in a puff of light and electricity, leaving a pair of fire trails behind from the red-hot tires. Doc excitedly cheers, but Marty is in shock, as it seems that Doc has just disintegrated Einstein.
Doc excitedly exclaims that he actually sent Einstein into the future... one minute into the future, to be exact. He also remarks excitedly that he built the time machine out of a DeLorean because it has style and because the steel body panels were a good conductor for the flux energy that propels the car through time. As if on cue, exactly one minute later, the DeLorean materializes where it disappeared, still traveling at the same speed as it was before, and screeches to a stop, now iced over. As Doc opens the door, Einstein is revealed to be alive and well, with his watch now one minute behind Doc's. Doc explains that Einstein likely believes that the trip was instantaneous, unaware of any change in time at all, skipping over that minute to instantly arrive at this moment and time. Doc shows Marty a device in the cabin called the "flux capacitor". It's the addition that makes time travel possible. Doc explains that, after an accident in his bathroom in 1955 where he hit his head, he had a vision of the flux capacitor. Though it took 30 years of research and most of his family's fortune to develop it; the project is a success and Doc plans to travel through time. As he talks to Marty, Doc absently sets the vehicle's destination time to that date, November 5th, 1955.
When Marty asks what the DeLorean runs on instead of gasoline, Doc tells him it needs plutonium, explaining that a nuclear reaction is necessary to generate 1.21 gigawatts to power the flux capacitor. Marty is alarmed, asking where the Doc could possibly have gotten such a substance and Doc tells him that he hired a couple of Libyan terrorists to steal it for him with the promise of building them a bomb. Doc, however, cheated them, delivering a fake bomb.
Doc and Marty, clad in yellow radiation suits, load another pellet of plutonium into the DeLorean and Doc begins his farewell address to Marty and the camera. It's interrupted though when a Volkswagen van races into the parking lot. A man pops out of the roof with an AK-47 and begins shooting . Doc yells for Marty to run; in the van are the Libyans that Doc cheated. Doc tries to hide as well but that is when the Libyans' van comes to a stop in front of him. Doc throws away his revolver, showing that he intends to surrender, only for the Libyan to shoot him full of holes. Marty screams and tries to hide but is found as well; when the Libyan tries to shoot him, his rifle jams. Marty jumps into the DeLorean and races off, the van close behind. As Marty swings back into the parking lot, he decides to see if the van can do 90 mph.
As he races towards a photo kiosk, Marty fails to see the speedometer creeping toward 88 mph or the fact that the time clock is set to November 5, 1955. Suddenly, there is a flash of light and the kiosk and parking lot are replaced with an empty grassy field, as the mall doesn't exist in 1955 and instead this space is taken up by the Twin Pines Ranch, whose owner Otis Peabody made valiant efforts to grow pine trees on the property. Marty has barely registered the change of scenery when the DeLorean plows through a scarecrow. This startles Marty, who loses control of the DeLorean, and crashes into Peabody's barn where his cows are housed. The noise wakes up the Peabodys in the farmhouse next door and they come outside to investigate the noise. When they open the barn doors, they are shocked at what they find: what appears to be an airplane without wings has crashed on their property. Peabody's son Sherman decides that the DeLorean is actually an alien spaceship, showing his family a comic book depicting an alien arrival as proof. Just then, the driver's door lifts up and Marty climbs out, still clad in his radiation suit. Peabody and his family scream in terror, thinking Marty is an alien, and flee towards the house.
Marty attempts to apologize for the damage, when suddenly Peabody returns with a shotgun and begins shooting at him. Marty jumps back in the DeLorean and speeds out of the barn, Peabody continuing to shoot at him. As Marty flees down the dirt path leading to the road, he inadvertently plows through one of two small pine trees protected by a picket fence. Peabody shoots at the car, in the process destroying his own mailbox, shouting, "You space bastard! You killed my pine!"
Marty reaches the main road and speeds off, muttering that the experience must be a nightmare, heading for home. When he gets to Lyon Estates, he finds the stone gates marking the entrance to the neighborhood, but to his surprise, instead of a street lined with houses, there is just an empty grassy field with several construction vehicles sitting idle, torn up dirt where the street is to be paved, and a large billboard advertising the future housing development which will be breaking ground in the next month.
Marty, still clad in his radiation suit, sees a car coming along the road and attempts to hitchhike, but the occupants are scared by Marty's suit and continue driving. Discovering that the DeLorean won't start, Marty removes his radiation suit and pushes the DeLorean back behind the billboard to hide it from passing motorists, then notices a sign reading "Hill Valley: 2 Miles."
After about an hour or so, Marty is able to make it to downtown Hill Valley. Hill Valley of 1955 is a lot different to Marty. The courthouse square is an actual garden instead of a parking lot, and contains a memorial to veterans of the Korean War. The Essex movie theater is showing Cattle Queen of Montana (1954) instead of a porno film. The town's record store advertises new records: 16 Tons by Merle Travis and The Ballad of Davy Crockett by George Brun. The Texaco station is a full service station where attendants not just fill up the tank but also wash the windows and check the customer's engine and tires. A mayoral campaign car drives around the square, blaring announcements on loudspeakers to remind residents to "Reelect Mayor Red Thomas!" Most importantly, the Courthouse Square clock tower is still functioning, as indicated when Marty is surprised to hear its half hour chime. Marty still believes that he is in a dream, but realizes this is reality when he picks up a newspaper tossed into a trash can and sees the date "November 5, 1955" on the top of the paper.
Marty steps into Lou's Diner (which will be the outlet for an aerobic class in 1985), at this point only inhabited by Lou Caruthers, the owner, and another customer eating breakfast at the counter. Marty goes to the phone booth and looks up Doc's address in the phone book, tearing the page out so he can look it up later. As Marty tries to ask for directions, Lou demands that Marty either order something or leave. Marty gets himself some decaf coffee after misunderstandings about Pepsi Free and Tab.
What Marty doesn't realize, as Lou is setting the coffee cup down, is that the customer he's sat down next to is his future father. He only realizes this when Biff shows up with his friends Match, Skinhead and 3D, to harass George. Biff has been forcing George to do his homework, something George has been slacking off on. When George admits that he hasn't completed Biff's homework, figuring that it is not due until Monday, Biff gets annoyed, and raps George on the head, reminding George that he will get expelled if he hands in his homework in George's handwriting. George finally agrees to finish up Biff's work and hand it over the next day, and Biff and his friends leave.
After Biff and his friends leave, the diner's busboy, Goldie Wilson (Donald Fullilove), chides George for letting Biff harass him all day. George insists that Biff is bigger than him, while Goldie points out that he doesn't expect to spend the rest of his own life working as a busboy, and he plans on becoming someone famous one day. Marty immediately recognizes Goldie and before realizing it, blurts out to Goldie that he's going to be mayor in 1985. This plants the idea in Goldie's mind and he begins to think about how as mayor of Hill Valley, and how he will clean up the town (to which Lou chafes "A colored mayor? That'll be the day", gives Goldie a broom, and tells him to start sweeping the floor).
After George leaves the diner, Marty's curiosity is piqued and he follows him into another neighborhood. He momentarily loses track of him until he finds George's bike parked beneath a tree. He looks up and notices George on a tree branch, using a pair of binoculars to spy on a girl getting undressed in her bedroom across the street -- Marty is shocked to find that George is a Peeping Tom. As he strains to get a better look, George suddenly slips and falls out of the tree, landing in the street in front of an oncoming Cadillac. Marty instinctively rushes out and pushes George out of harm's way. The car slams on its brakes, but it hits Marty, who hits his head on the pavement and is knocked unconscious. George gets on his bike and rides away as Sam Baines, the driver, yells to his wife that another kid has jumped in front of his car.
When Marty comes around, it's night time and it is raining outside, and he is lying in an unfamiliar bed. His mother's voice tells him that he's been out for nine hours. Marty, still semi-conscious, quips about having a dream that he went back in time. Lorraine's voice reassures him that he's safe and sound in 1955. This prompts Marty to bolt upright just as a lamp is turned on, and he is dumbstruck to see Lorraine, in 1955 a very attractive teenage girl. Lorraine introduces herself and begins to hit on Marty almost immediately, thinking his name is "Calvin Klein" because that's the brand of underwear Marty is wearing (and she may have been the one to take his pants off). Marty instinctively panics when Lorraine tries to make advances on him and looks like she is trying to kiss him. Fortunately for Marty, this is interrupted when Lorraine's mother Stella calls her down for dinner.
At dinner, Marty meets the rest of Lorraine's siblings, including her brothers Milton and Toby, her sister Sally, and in the crib nearby, little baby Joey. Stella admits that Joey loves his crib, and cries every time they try to take him out. Marty recognizes Joey as the future prison inmate, and can't resist the urge to joke to the baby to "Better get used to these bars, kid..." The family eats while watching an episode of "The Honeymooners" on the new television set that Sam has just brought home. Marty immediately recognizes the episode they are watching as one he has watched in 1985, which he explains by saying that he saw it in a rerun, a word that puzzles Lorraine's younger brother. Marty asks how to find Doc's address, which Lorraine's father says is over on the east end of town. Marty knows that area as "John F. Kennedy Drive", a name that Lorraine's father doesn't know because John F. Kennedy won't be President for another six years. As Marty leaves the house, Sam says that Marty's an "idiot" & warns Lorraine that if she ever has a kid like Marty, he will disown her.
Marty makes his way over to Doc's house (which will be destroyed in a fire sometime in the next 30 years, which is why Doc lives out of his garage in 1985). Doc, who does not recognize Marty, answers the door, with a bandage on his forehead from where he hit his head trying to hang a clock above his toilet (the incident that gave him the vision of the flux capacitor). Without saying a word, he immediately hooks Marty up to his newest invention - a thought reader. Doc determines that Marty comes from a great distance, and wants him to make a donation to the Coast Guard Youth Auxiliary.
Frustrated, Marty tells Doc directly that his time machine works and he is from the future. Doc is skeptical, even when Marty shows him his future driver's license and a family photo. Doc comments that the photo must have been forged as Dave's hair is missing from the picture. However, Marty is able to convince Doc of the truth by mentioning the wound on his head that prompted the vision of the flux capacitor. To prove that Doc has invented it, Marty has Doc drive him out to the place where he's hidden the DeLorean. Doc is overly delighted when he compares the drawing he made of a flux capacitor and sees the real device installed on the DeLorean.
After returning to Doc's estate, they manage to plug in Marty's "portable television studio" to see the video Marty had filmed in 1985. Doc becomes quite excited and panicky when they reach the point on tape where he will say that time travel requires 1.21 gigawatts of energy from the plutonium to power the flux capacitor. Doc explains that plutonium is very hard to come by in 1955 and that the only energy source capable of that amount of power is a lightning bolt. Predicting the strike zone of a lightning bolt is impossible and Doc tells Marty he may be stuck forever in 1955. But then Marty remembers the flyer the woman gave him and Jennifer about the lightning bolt that is going to strike the clock tower at exactly 10:04 PM next Saturday night and hands it to Doc.
Now that he knows a date and time, Doc begins working on a plan to harness the power of the bolt and send Marty home. When Marty says he can hang out in 1955 for a week, Doc objects, warning him that it could be detrimental to future history and jeopardize his entire existence. He asks Marty if he had any interaction with anyone in the last few hours and Marty drops the bomb about preventing the first meeting between his father and mother. Doc asks to see the photo of Marty and his siblings again; Dave's head is now completely gone. This means that in order to go back to 1985, Marty first needs to make his parents fall in love and have their first kiss within a week.
Doc takes Marty to the high school the next morning. Marty is amazed to find that there is no graffiti on the building, unlike in 1985. After peeping through a classroom window and watching Lorraine cheating on a test, they spot George in the hallway during a passing period, seeing him being picked on (in part because of the large "KICK ME" note that one of Biff's gang taped to his back). George is further demoralized when Strickland (who in 1955 is down to his last dregs of hair) appears and tells him he's a slacker. Doc is baffled that Lorraine could fall in love with someone like George, and Marty admits that his best guess is she originally felt sorry for him after her dad nearly killed him. Doc recognizes their relationship as a version of the Florence Nightingale effect, which happens when nurses develop romantic feelings for their patients.
Marty tries encouraging George to talk to Lorraine, however, an attempt to simply introduce them to each other fails because Lorraine is already smitten with Marty. Doc finds that the situation is more serious than they'd thought; George lacks the self-confidence to ask Lorraine out, as he fears that he couldn't handle a rejection if she said "no", and getting them together permanently could be impossible. At lunch, Marty tries again to convince George, by saying Lorraine has been talking about him and that he should ask her to the Enchantment Under the Sea dance. George spends his lunch by himself writing science fiction short stories. Marty asks to read one of them and George refuses, saying he's afraid people would be critical. He also suggests that Lorraine may want to go with someone else to the dance, namely Biff, who is across the cafeteria, sitting with Lorraine and trying to grope her. Marty immediately marches over to them and pulls the much larger Biff off his mother. Biff begins pushing Marty, however, Marty, unlike his meek father, begins pushing back and is about to fight Biff when Strickland breaks it up.
Marty follows George home and begins pleading with George to ask Lorraine out. George continues to refuse and tells Marty that no one in the world will make him change his mind. That night, Marty sneaks into George's room in his radiation suit, places his Walkman headphones on George and gives him a blast of ear-splitting Eddie Van Halen guitar riffing. Marty claims he is Darth Vader, an extraterrestrial from the planet Vulcan, and intimidates George into asking Lorraine out, threatening him with a "brain melting gun" (actually a hairdryer). To keep George from calling for his parents, Marty chloroforms him, before jumping out the window and into Doc's car.
The next day, George rushes up to Marty at the Texaco station, disheveled and frantic, having overslept, while Marty is trying to open a Pepsi -- George pops it open with the bottle hook on the machine. George knows he needs to ask Lorraine out but he doesn't know what he should say. Marty takes George back to Lou's diner, where Lorraine is hanging out with her friends. Marty suggests to George that he tell Lorraine, "Destiny has brought me to you." George orders a chocolate milkshake to calm his nerves before approaching Lorraine. It gets off to a shaky start when, in a fit of nervousness, George accidentally mangles the lines Marty gave him. Though Lorraine seems charmed by him, George's attempt comes to a grinding halt when Biff and his friends come in to toss him out. As Biff demands money from George, Marty, sitting at the counter, "accidentally" trips Biff. Biff turns his anger on Marty, and is about to punch him when Marty tricks him into looking away, giving Marty the opportunity to punch Biff and bolt out the door.
Once outside, Marty steals a passing boy's scooter, tears off the crate and turns the bottom into a skateboard. Biff and his goons chase Marty in Biff's car around the town square. Marty is able to avoid serious injury. While riding on the hood of Biff's car, he distracts them by suddenly jumping up, jumping over the hood, the windshield and the backseat, and then hopping off onto the waiting skateboard at the rear. Biff and his friends are confused, and then see they are barreling towards a manure truck parked on the curb. They can only shout "SHIIIIT!!!!!" as the car slams into the back of the truck, which dumps its entire load of manure on them. Watching the chase from the diner, Lorraine becomes even more attracted to the adventurous Marty.
Back at Doc's shop, the inventor shows Marty how he'll use the lighting bolt to power the DeLorean. He'll string heavy cable from the clock down to the street, building a circuit. A long rod attached to the back of the DeLorean will channel the energy from the bolt directly into the flux capacitor. The timing will have to be precise. The demonstration goes well, though it sets a garbage pail on fire. As Doc uses a fire extinguisher to put out the flames, they are interrupted by a knock at the door. To Doc's shock, it's Lorraine, who has followed Marty. Doc and Marty quickly cover the DeLorean with a tarp before letting Lorraine in. Lorraine asks Marty if he wants to be her date to the Enchantment Under The Sea Dance. Marty attempts to back out, suggesting she go with George, but Lorraine balks at the idea, saying a real man stands up for the woman he loves, referring to the fight Marty just had with Biff.
Marty suddenly sees a way to get George to win Lorraine's heart. He approaches George while George is doing his parents' laundry, and tells him to find him with Lorraine in Doc's car in the school parking lot at a certain time, where Marty plans to appear to "take advantage" of her, which he believes will make her angry. George is to pull Marty out of the car and pretend to beat him up, proving that he's the bigger man.
The night of the dance arrives. George is already there, in a tux, waiting for his cue, as the all-black band known as the Starlighters performs on the stage. At Lou's Diner, Marty writes Doc a letter on a piece of stationary warning. He slips the note into the pocket of Doc's coat while Doc is in the middle of using $50 to bribe a cop who asks him if he has a permit for his "weather experiment".
Marty arrives at the dance in Doc's car with Lorraine. As they stop, he asks her if they can "park" for a while. To Marty's astonishment, Lorraine produces a small bottle of whiskey and begins to smoke, two bad habits she has in 1985. Marty warns her she may regret it later and Lorraine dismisses it, exasperated that Marty sounds like her mother. She also is aggressive in coming on to Marty in the car, much more than Marty had anticipated, though when she kisses Marty rather hard on the lips, she admits afterwards that she feels like she's kissing her brother.
Just then, the door is opened and Marty is pulled roughly from the driver's seat. But to Marty's shock, it's not George. Rather, it's Biff, drunk, and seeking revenge for the $300 in damages Marty inflicted on his car in the manure truck accident. When Biff sees Lorraine in the car, however, he throws Marty to Match, Skinhead and 3D, climbs into the car, and begins to molest her. Match, Skinhead and 3D take Marty out behind the school and toss him into the open trunk of the first car they see, then slam the lid shut. Unfortunately for them, the car belongs to Marvin Berry and the Starlighters. They scare Biff's gang off and they realize that the keys are in the trunk with Marty.
George arrives at Doc's car, opens the door as planned, and delivers the lines Marty told him, but is taken off-guard realizing that he is not only dealing with Biff, but his "rescue" is now the real deal. He takes a half-hearted punch at Biff, who grabs his arm and begins to twist it. When Lorraine pleades with Biff and tries to intervene, Biff roughly pushes a Lorraine off and onto the ground and begins laughing, George summons up the strength and courage, curls his left hand into a fist, and punches Biff squarely in the jaw, knocking him out. Marty, freed from the trunk thanks to Marvin Berry himself, races to the scene just in time to see Biff slump to the ground at George's feet. George takes the grateful Lorraine's hand and the two go into the dance hall.
Marty, knowing that his future isn't sealed until George kisses Lorraine, goes back to the band and finds that Marvin is unable to play guitar having injured his hand while freeing Marty from the trunk. Marty agrees to play guitar in Marvin's place and the band strikes up again, playing a romantic song ("Earth Angel"). Marty, already weak because his parents' love is not confirmed, begins to fade into non-existence when a fellow student cuts in between George and Lorraine on the dance floor, however, George regains his courage, takes Lorraine back and kisses her passionately. Marty is instantly revived and finishes the song and sees his mother and father happily in each others arms.
Berry asks Marty to play another number with the band. Reluctant at first, Marty can't resist the opportunity and launches the band into "Johnny B. Goode". While Marty plays, Marvin Berry calls his cousin Chuck (the soon-to-be-famous rock n' roll star), telling him that he found the "new sound" Chuck was looking for. Marty does Chuck Berry's trademark duck walk, and then gets carried away imitating other guitar heroes - windmilling his arm and kicking over his amplifier in imitation of Pete Townshend, lying on the stage kicking his legs in imitation of Angus Young, playing behind his head like Jimi Hendrix, and tapping in the style of Eddie Van Halen. In the face of uncomprehending stares from the audience, while lost in heavy metal riffing, Marty stops and tells the students "I guess you're not ready for *that*. But your kids are gonna LOVE it." Marty turns to leave the dance and runs into George and Lorraine. Lorraine asks if it's OK for George to take her home and Marty heartily agrees. He also advises them that if they have a son who accidentally sets fire to the living room rug when he's eight years old, to go easy on him, implying that he's talking about himself
At the town square, Doc waits impatiently for Marty. Marty arrives, saying he needed time to change back into his 1985 clothes. As they prepare for the event, Doc discovers the note from Marty in his pocket. Refusing to know too much about his future, he tears up the note without reading it. Just then, a falling tree limb disconnects the cable he has installed from the clock tower to the street. Doc climbs again to the clock tower and has Marty feed him the cable. Marty also tries to warn Doc about his death but is drowned out by thunder. Marty runs back to the DeLorean and races off to the starting point Doc has painted for him. While waiting for the timer to go off, wishing he had more time, then realizing that he has all the time we wants because he's in a time machine, he resets his destination time to arrive 11 minutes earlier than he left so he can warn Doc. Just then, the car stalls and Marty frantically tries to start it again. When it does restart, after the timer goes off, Marty begins speeding toward the town square. Despite some difficulty, Doc reconnects the cable just as the lighting bolt surges through the line and the DeLorean speeds off into the future, leaving behind a pair of fire trails. Doc celebrates joyously in the street.
Thirty years later, at 1:24 AM, a homeless bum is seen sleeping on a bench in the town square when he is woken up by three sonic booms, just as the DeLorean materializes and slams into the porno theatre just down the block. The bum, Red, quips "Crazy drunk drivers." Marty backs the DeLorean out and turns around, only for the car to promptly ice up from the time travel trip. Just then, the Libyans' blue VW minibus passes by, driving recklessly. Marty jumps back into the DeLorean only to have it stall on him again.
Marty is forced to run to the mall where the initial experiment is taking place. As he arrives, we see that the sign now reads "Lone Pine Mall," showing that Peabody never regrew the pine tree that Marty destroyed. He sees Doc get shot, again and watches from a distance as the Libyans chase his previous self around the parking lot. When the DeLorean vanishes and Marty's counterpart goes back to 1955, the Libyans lose control of their van, which and crashes into the photo kiosk & tips on its side, trapping the Libyans. Marty runs down to Doc. Marty is devastated that he couldn't arrive in time to save Doc. Doc, however, suddenly sits up. Marty is stunned until Doc opens his shirt, revealing that he's wearing a bulletproof vest. Marty asks him about the consequences of changing the future and the space-time continuum and the Doc admit, "Well, I thought, 'What the hell!'". Doc drives Marty home and tells him he plans to venture about 30 years into the future. He then ramps the DeLorean up to 88 mph and drives off into the night in a flash of light.
Marty wakes up the next morning to find that the furniture in his house is arranged differently. Dave is wearing a suit and working an office job. Linda seems to be having trouble keeping track of all the teenage boys who keep calling her for dates, much to Dave's exasperation. George and Lorraine arrive home from a tennis match, happy and even a bit frisky. Lorraine asks Marty about the camping trip he has planned with Jennifer, to which Marty mentions that the car is wrecked. Everyone starts barking about it until George shows them that Biff is waxing the car, a late model BMW, in the driveway. Biff now runs an auto detailing service and now is working for George, rather than the other way around. George seems amused at Biff's efforts to get away with as little work as possible (but now confronts Biff to complete the work he was hired for; two coats of wax instead of only one). Biff jokingly says that he'll complete the work properly.
Moments later, Biff comes into the house carrying a box filled with copies of George's first published book, the cover of which resembles Marty's appearance in the radiation suit. Marty is unsure how to take everything in when Biff hands him a set of keys. They are for the Toyota pickup truck he'd been thinking about purchasing with Jennifer back at the beginning of the movie. As Marty goes into the garage and looks at the truck, quite astonished that the future had been altered so dramatically for himself and his family, Jennifer appears behind Marty. He's relieved to see her and happy that his family is happier as well.
Suddenly there is a burst of electricity and the DeLorean screeches to a halt. Doc gets out, dressed in wild clothing and tells Marty he needs to come with him to the future; something is wrong with his and Jennifer's kids. Doc gathers "fuel" by rummaging through a garbage can and loads it into a new addition to the car's engine called Mr. Fusion. All three pile into the DeLorean and it backs out of the driveway. Marty tells the Doc he needs to back up further to get up to 88 mph, as they have no road. Doc replies, "Roads? Where we're going, we don't need roads!" Doc has converted the car to a hovercraft. The car takes off, and flies at the camera... and the words "To be continued..." flash on the screen.