A text crawl after the opening credits explains that in the near future, the technology that created synthetic humans has entered into the 'Nexus phase': Replicants, sophisticated androids that are virtually identical to humans, are now superior in strength and at least equal in intelligence to their creators. Replicants are designed and built by the Tyrell Corporation, a giant multiconglomerate headquartered in two pyramid-like towers. The latest and most advanced version of Replicant technology is the Nexus 6 model. Replicants are mostly used as slaves for manual labor on the "Off-World Colonies" out in space. Following a violent mutiny by Replicants on an Off-World Colony, the androids were outlawed on Earth. Specialized police units, "Blade Runners", are charged with the difficult task of detecting Replicants who illegally come to Earth. If found, Replicants are executed, which is not considered murder but euphemistically called "retirement."
The opening title sets the story in Los Angeles in November, 2019. LA and the surrounding area have become heavily industrialized, crowded with people, and rain falls constantly. Apart from ground traffic, there are flying personal vehicles called 'spinners' soaring through the sky.
At the Tyrell Corporation, a Blade Runner, Holden (Morgan Paull), is interviewing a new employee using a special device called a Voight-Kampff (VK) analyzer. The machine is designed to detect any physical responses in the test subject in response to questions that are deliberately meant to affect the subject emotionally. After a few questions, the man being tested, Leon Kowalski (Brion James), becomes obviously agitated and eventually hostile, shooting Holden.
Rick Deckard (Harrison Ford), a former Blade Runner, is eating on the street at a Japanese noodle bar when another man, Gaff (Edward James Olmos), tells him he's under arrest. Deckard tries to ignore the man but when he hears that a man called 'Bryant' is asking for him, he eventually agrees to come. Gaff flies Deckard by spinner to police headquarters and delivers Deckard to his old boss, Bryant (M. Emmet Walsh). Bryant tells Deckard that there are four "skin jobs" (the derogatory term for Replicants) loose on the streets, and he needs Deckard to retire them. Deckard suggest that they give the job to Holden, but Bryant says they already did that: "he can breathe okay, as long as nobody unplugs him." Deckard is not interested and tries to leave, but Bryant successfully blackmails him into accepting with a veiled threat.
They watch footage of Leon's VK test as Bryant explains that six Nexus-6 Replicants murdered 23 people on an Off-World colony and then stole a shuttle to Earth. Two of them were killed three days before by a high-voltage security fence while trying to break into the Tyrell Corporation, the other four have survived and disappeared. Suspecting that they might try to infiltrate the Tyrell Corporation, Holden was tasked with testing their new employees, and nearly died after identifying one. Why the Replicants risked returning to the Tyrell Corporation remains a mystery. Bryant shows Deckard their files. The leader is Roy Batty (Rutger Hauer), the most advanced and intelligent of the group. The others are Zhora (Joanna Cassidy), a trained Off-World assassin; Pris (Daryl Hannah), a 'pleasure model' (probably used for prostitution); and Leon, the Replicant who shot Holden. Bryant also tells Deckard that although the Nexus-6s are designed without emotions, they are believed to be advanced enough to develop these themselves within years, including hate and anger. As a fail-safe, the scientists designed the Nexus-6s to have only a four-year lifespan. Bryant sends Deckard to Tyrell Corp.'s headquarters to test the VK machine on one of their Nexus-6s, but Deckard wonders if their design might make them impossible to detect.
Deckard and Gaff fly to Tyrell headquarters. While Deckard awaits Dr. Tyrell, he is welcomed by Rachael (Sean Young), a beautiful woman and Tyrell's personal assistant. Dr. Eldon Tyrell (Joe Turkel) appears and questions Deckard about the Voight-Kampff test, doubting its ability to distinguish Replicants from humans. Tyrell offers Rachael as a test subject, saying he wants to see a negative test result on a human before providing a Replicant to be tested. Deckard asks Rachael over 100 test questions before the VK machine finally alerts him that she is a Replicant. Tyrell asks Rachael to leave. Deckard is surprised, because it usually takes 20 to 30 questions to identify a normal Replicant; Tyrell reveals that Rachael is unaware that she is one, although she may be beginning to suspect. He explains that Replicants may become emotionally unstable because of the short time they have to learn basic experiences. Rachael is an experimental Replicant who has been designed with implanted memories; the memories serve as a buffer for the emotions, which allows Replicants to better control their behavior.
Deckard proceeds to the address that Leon gave in his VK test. In his apartment, he finds a stack of family photographs there, as well as a scale from an animal's hide. He is not aware that Leon is watching the police from a short distance. Not far away, Roy Batty is waiting on the street for Leon to return from his apartment. Leon appears and tells Roy that there were policemen there and he was unable to retrieve his photographs. Roy is perturbed but takes Leon with him to a shop called Eye World, owned by a Chinese man named Hannibal Chew (James Hong), who engineers Replicants' eyes for Tyrell. He is confronted in his subzero lab by Roy and Leon, the latter of whom rips open Chew's thermal coat to make it easier for Roy to interrogate him. Roy asks Chew about "incept dates," the date marking a replicant's first activation and beginning of their four year lifespan. Chew, quickly freezing to death, has no knowledge about that, and desperately tells them that they need to talk to Tyrell about increasing their lifespans. Roy suggests that meeting with Tyrell will be difficult, but Chew tells him that a Tyrell employee, J.F. Sebastian, may be able to gain Roy access.
Deckard takes Leon's stack of photos home with him. He is surprised by Rachael in the elevator. Deckard, seemingly feeling caught off-guard, is quite rude to Rachael, who learned what Tyrell revealed to Deckard about her, but Tyrell refused to see her afterwards. She has come to debunk his claims, and shows Deckard a picture of herself with her mother. Deckard insensitively quashes Rachael's insistence that she has an actual past, giving her detailed descriptions of several of her 'childhood memories'. He tells her that these have been taken from other people, especially Tyrell's niece. She is extremely hurt and starts crying, so Deckard fetches her a drink, but she has left by the time he is back.
In another part of Los Angeles, near an old, neglected hotel called the Bradbury, a woman walks into an alley and covers herself with waste paper to keep warm. She dozes for a bit until a man approaches her and startles her awake. She runs away, breaking the window of his van, but the man kindly returns one of her bags and she becomes friendly. The woman is revealed to be Pris, one of the Nexus-6s Deckard is pursuing. The man is J.F. Sebastian (William Sanderson), a genetic designer for the Tyrell Corporation and the person Chew told Roy to find. Pris agrees to stay at Sebastian's hotel, where he lives alone and designs lifelike toys and dolls. Pris tells him that she is an orphan, but she has a few friends who may come over.
In his apartment while drinking, Deckard examines his old photographs on his piano. In the Final Cut and Director's editions, he briefly dreams of a white unicorn. When he awakens, he analyzes one of Leon's photographs in a scanning device, and finds that a girl, probably Zhora, is visible in a back room. Deckard notes that she has a prominent tattoo in her neck of a looped serpent.
Deckard visits the crowded streets near Chinatown and has a old Asian woman examine the animal scale. Deckard believes it to be from a fish but it's from a snake and, like most animals of the time period, is artificial. A serial number is also visible under the microscan; it identifies the maker as a man named Abdul Ben Hassan (Ben Astar), whose shop is right up the street. Deckard confronts Hassan, who tells him he has made a snake for a club owned by Taffey Lewis (Hy Pyke). Deckard goes to the club and unsuccessfully tries to pressure Lewis into identifying the girl in Leon's picture. He places a quick call to Rachael, apologizing for his insensitivity and asking her if she'd like to join him at the club. Rachel refuses, saying it is not her kind of place.
Deckard finds that Zhora poses as an exotic dancer named Miss Salomé at the club, and she uses an artificial snake during her performances. After the show, Deckard poses as an irritating union representative, claiming to investigate abuses by club owners who may spy on female performers in their dressing rooms through peepholes drilled into the walls. Zhora sees through Deckard's ruse, beats him violently and is almost at the point of killing him, until she is disturbed by a few other dancers entering the room. She dashes from the club into the overcrowded streets, trying to hide in traffic. Deckard quickly catches up and chases her until he's able to shoot her. Zhora crashes through several plate glass windows and falls to the street, dead. Deckard identifies himself to the police that respond to the incident and when a passerby examines Zhora, they see the snake tattoo under her ear.
Bryant arrives on the scene and talks to Deckard, congratulating him for finding and retiring Zhora. He tells Deckard that there are four more Replicants to retire; Deckard insists that there are only three left. Bryant tells him that Rachael has disappeared, so Deckard now has to retire her as well. Deckard leaves, and spots her a few moments later across the street. As he follows her, he's suddenly grabbed by Leon, who knocks his pistol away and beats him severely. When Leon says "Wake up! Time to die!", and is poised to stab his fingers through Deckard's eyes, his forehead explodes; he has been shot by Rachael using Deckard's own pistol. Deckard returns to his apartment and Rachael joins him.
Rachael seems to have accepted the truth about herself, and Deckard appears to be much more sympathetic toward her since she saved him from Leon. He gives her a drink and as he cleans himself up, she asks him if he'd hunt her down, should she disappear to the north; he tells her he wouldn't, but someone else surely would. She asks if he knows more about her incept date and her lifespan, but Deckard says that he didn't look at them. Rachael asks him if he has ever tried the VK test on himself, but Deckard has fallen asleep on his couch. Rachael starts playing on his piano. Deckard wakes up, and the two play together. Rachael says she remembers piano lessons, but these memories are probably Tyrell's niece's, not hers. Deckard becomes more amorous, but Rachael gets insecure and rejects his advances. Deckard prevents her from leaving his apartment; she admits that she doesn't know how to make love, so Deckard 'instructs' her step by step, and they make love.
Pris wakes up in Sebastian's apartment. She talks to her host about his strange skin condition, "Methuselah syndrome," which makes him age quickly -- he is only 25, but his wrinkled skin makes him look much older. It is the reason why he can't leave Earth for an Off-World colony, but he doesn't mind. Suddenly, Roy appears, summoned there by Pris. He sadly shares the news that Zhora and Leon are both retired. Roy and Pris reveal to Sebastian that they are both Nexus-6s and they need his help. Pris proves to Sebastian that she's artificial by grabbing an egg from boiling water and tossing it to Sebastian, who finds it too hot to handle. They claim to have a similar disease as he does, accelerated aging; Pris will need help, or she'll die. Sebastian says that he only does genetic design, but Roy notices that Sebastian plays chess and asks him about his opponent, who is Tyrell himself. Roy gently coerces Sebastian to use his connection to Tyrell to arrange a personal meeting. Sebastian reluctantly agrees.
Roy and Sebastian go to Tyrell's pyramidal home and take an elevator to his penthouse. They are stopped as a security measure, but are allowed to proceed when Sebastian voices two moves to Tyrell himself that win the chess match they'd been playing; the last move is given to him by Roy. Tyrell is fascinated by the bold move, and invites Sebastian in. In Tyrell's bedchamber, Sebastian introduces Roy, but Tyrell seems to have been expecting Roy for some time. Roy confronts his creator, saying specifically that he wants an extension of his short lifespan, and calls Tyrell "father." (In the 1982 Theatrical and 1992 Director's editions, Roy says "fucker" in place of father.) Tyrell explains that he is unable to do that; once an artificial being like Roy has been completed, it is impossible to make any alterations in its lifecycle. Roy proposes several biological interventions to prolong his lifespan, but Tyrell dismisses all of them as ineffective, saying that they have made him as well they could, though not to last. Roy becomes despondent, but Tyrell comforts him, saying that "the light that burns twice as bright burns half as long, and you have burned so very very brightly". Roy tells Tyrell he's done "questionable things", but Tyrell's pride seems too big for him to care, focusing on the extraordinary things Roy has done. Roy, still despondent, first kisses Tyrell, then begins to crush his skull, poking his thumbs through his creator's eyes. Tyrell falls dead, witnessed by a horrified Sebastian.
Deckard is in his car on the streets, moving it when some street people climb on the back, apparently hoping to scavenge parts they can sell. He receives a report from Bryant, who tells him that Tyrell is dead and Sebastian has been found dead at the same scene. Deckard places a call to Sebastian's apartment, claiming to be a friend. Pris answers the call but hangs up without a word. Deckard drives to Sebastian's apartment and searches for evidence or leads. As Deckard searches the cluttered mess of puppets and mannequins, he is surprised by a disguised Pris, who assaults him using acrobatics. As she performs a series of back flips to finish Deckard off, he shoots her through the abdomen. She spasms violently for a few moments before Deckard shoots her twice more and finally kills her.
Deckard hears Roy arrive, and takes up position in a nearby room. Roy comes in and finds Pris dead. He weeps and and kisses her lifeless lips. He enters the next room; Deckard shoots at him but misses. Roy chides him that he's "not being very sporting to fire on an unarmed opponent." A game of cat-and-mouse starts, with Roy stalking Deckard throughout the apartment. At one point, he seizes Deckard's hand through a wall and deliberately breaks two of his fingers, in retaliation for Zhora and Pris. He gives him the gun back and releases his hand, but Deckard finds it impossible to shoot straight with two broken fingers. Roy gives him a few seconds head-start to flee. Deckard escapes to an upper floor in the building, but is easily found by Roy when he howls in pain from trying to reset his fingers. Deckard keeps moving, but is in great pain and drops his gun. Roy is already showing signs of his own impending death -- he stabs himself through the hand with a large nail to temporarily stabilize his condition. Deckard seizes an opportunity to beat Roy with a large pipe but he cannot incapacitate Roy, whose superhuman strength is too much for Deckard. Deckard eventually escapes onto a window ledge and climbs to the roof, but Roy appears moments later, holding a white dove he found on the roof. Deckard tries to escape by jumping to another roof across the street, but barely makes it to the ledge. He nearly plummets, hanging on by one hand. Roy makes the jump quite easily and peers over the ledge at Deckard, saying "Quite an experience to live in fear, isn't it? That's what it is to be a slave". Deckard slips and Roy catches his arm with one hand, pulling him up to safety. Roy sits down near him, and tells Deckard that he's seen more in his short life than most humans would see in a full lifetime. Roy is saddened by the idea that all the memories he's acquired will be lost "like tears in rain." Then, echoing the last thing Leon said to Deckard, Roy says "time to die" -- but he's referring to himself. As he finally dies, the dove in his hand flies off. In the Final Cut (2007), the rain continues and the dove flies toward an overcast sky.
In the original theatrical version (1982), the rain has stopped and the dove flies toward a clear blue sky. Deckard muses that he doesn't know why Roy saved him; perhaps he had a newfound love for life, including Deckard's. He notes that the Replicants only wanted the same answers that humans do about life: where do we come from and how long.
Gaff meets Deckard on the roof and throws his pistol back to him. He congratulates Deckard on completing his investigation; Deckard tells him he's officially finished with hunting Replicants. As Gaff walks away, he looks back over his shoulder, and yells, "It's too bad she won't live, but then again, who does?", referring to Rachael.
Deckard returns to his apartment and is alarmed to find the door ajar. He takes out his gun and calls Rachael. When she doesn't answer he walks through the rooms with his gun drawn. In the bedroom, Rachael is completely covered by the sheet. He fears that she is dead. Much to his relief, she wakes up when he pulls the sheet back and touches her. He asks her whether she loves and trusts him; she replies that she does. A few minutes later, she is dressed and Deckard, after checking the lobby outside his apartment, motions for her to join him in the elevator. On the floor of the lobby is a small origami unicorn, left there by Gaff. Gaff's words about Rachael not living echo in Deckard's head. He realizes that Gaff was there but let Rachael live. Deckard studies the unicorn for a moment, then crushes it in his hand. In the Final Cut and Director's (1992) editions, the film ends when the elevator doors close.
In the Theatrical edition, Deckard and Rachael drive into a sun-lit and mountainous area, and Deckard explains in voice-over that Tyrell told him that Rachael was special, and has no termination date. Echoing Gaff's sentiment atop the roof, he muses, "I didn't know how long we had together... who does?"