Plot

After two of the devil's three sons escape Hell to wreak havoc on Earth, the devil must send his third son, the mild-mannered Nicky, to bring them back before it's too late.

When somebody's mother is an angel and his father is the devil, life can be really confusing. For a sweet boy like Little Nicky, it just got a whole lot worse. His two evil brothers Adrian and Cassius have just escaped from Hell and are wreaking havoc on an unsuspecting earth. His dad is disintegrating and it's up to Nicky to save him and all of a humanity by midnight before one of his brothers becomes the new Satan.—Anthony Pereyra {hypersonic91@yahoo.com}

Little Nicky is "daddy's little girl" in Hell. He's the son of Satan, who got the job from HIS father, Lucifer. Satan wants to retire, but none of his sons are good enough for the job. There's Cassius, who's big and strong, but lacks the 'goodness' to make the job real. There's Adrian, who while really hot (no pun intended) and smart, has no goodness at all. Then there's Nicky [Sandler] who, while having good, lacks any evil whatsoever. As seen in the previews, he is told to release his evil. He needs to release it to save his dad. Cassius and Adrain leave Hell, thereby freezing the wall of fire that lets the damned souls into Hell. Since no souls can come in now, Satan starts to die. It's up to Little Nicky to go and get his brothers, putting them into a flask and bringing them back to Hell at the exact same time to save Satan from decomposition. If Nicky 'dies' on Earth, he will be able to get through the frozen wall and back up to Earth. The catch is that he has only a week, and that Adrian and Cassius are MUCH more powerful than he is.—Liz Skywalker <lizskywalker@hotmail.com>

After the lord of darkness decides he will not cede his underworld throne to any of his three sons, the two most powerful of the three escape to Earth to create a kingdom for themselves there. This action closes the portal filtering sinful souls to Hell and causes Satan to begin withering away. He must send his most weak but beloved son, Little Nicky, to Earth to return his brothers to Hell. Can Nicky learn his way around Earth and round up his brothers in time to save Satan?—FMJ_Joker

The story revolves around a struggle to determine which of Satan's (Harvey Keitel) three sons will succeed their father as ruler of Hell. Adrian (Rhys Ifans) is the most devious, Cassius (Tom Lister Jr.) is the cruelest and Nicky (Adam Sandler) is their father's favorite. Adrian and Cassius claim that Nicky's mother is a goat and torment him by controlling his body with their minds. Nicky has had a speech impediment and a disfigured jaw since Cassius hit him in the face with a shovel when he was a child.

Having been the "Prince of Darkness" for ten thousand years, Satan assembles his sons to decide which of them will succeed him, but instead he keeps the throne for himself because his sons are not yet ready to be his successor and tells them that they need to learn to keep the balance between good and evil. Angered by this decision, Adrian and Cassius go to Earth to create a new Hell by possessing religious and political leaders in New York City. As they leave, they freeze the entrance to Hell, preventing more souls from entering and causing Satan's body to begin decomposing. To stop Adrian and Cassius, Satan sends Nicky to Earth with a silver flask that traps whoever drinks from it inside.

At first, Nicky has trouble staying alive on Earth. He is killed several times, landing in Hell and returning to New York each time. While learning how to eat and sleep, he meets a talking bulldog named Mr. Beefy (voice of Robert Smigel), rents an apartment with an actor named Todd (Allen Covert) and falls in love with a design student named Valerie (Patricia Arquette).

Nicky's first encounter with his brothers occurs when Adrian sees him with Valerie, takes mental control of his body and makes him scare her away. Then Nicky sees Cassius on television, possessing the referee (Dana Carvey) of a Harlem Globetrotters game. When he goes to the court and tricks Cassius into the flask, Satanist metal-heads John (Jonathan Loughran) and Peter (Peter Dante) are so thrilled with his performance that they become his devoted fans. That evening, Nicky tries to apologize to Valerie. The meeting goes badly at first, but she accepts him after he explains who he is and why he is on Earth.

The next day, Adrian possesses the Chief of the NYPD (Michael McKean) and accuses Nicky of mass murder using an edited scene from Scarface. Not knowing what to do, Nicky has Todd kill him so he can go back to Hell and ask his father for advice, but his father has trouble hearing because his ears have fallen off and his assistants are in a panic because the midnight deadline to capture Adrian and Cassius is only hours away. Back on Earth again, Nicky and his friends devise a plan to capture Adrian in a subway station, but Adrian discovers their trick. In the ensuing fight, Adrian grabs Valerie and dives onto the track as a train approaches, but Nicky throws her out of the way, leaving himself and Adrian to be killed by the train.

Arriving in Hell just minutes before midnight, Adrian dethrones his weakened father and takes over, rising into Central Park and starting a riotous party while all of the demons except Satan's assistant Jimmy (Blake Clark) join Adrian on Earth. Meanwhile, Nicky wakes up in Heaven as a reward for sacrificing himself and meets his mother Holly (Reese Witherspoon), an angel who tells him he can defeat Adrian with the "Inner Light" he inherited from her. After she gives him a mysterious orb, he goes to Central Park.

The demons discover Nicky and try to attack him, but Nicky creates gifts for them which makes them respect Nicky enough to join him and stop Adrian, but when Adrian kills one, they all run away. Nicky and Adrian then fight, which results in both of them sucked into the flask where they have a three-way battle with Cassius. Adrian appears to win a pitched battle by locking Nicky in the flask and turning himself into a bat, but Nicky escapes from the flask. When he shatters the orb, Ozzy Osbourne appears, bites Adrian's head off and spits it into the flask.

With his brothers captured, Nicky is ready to save his father. After he sins to make sure he goes to Hell, he and Valerie express their love for each other, and she kills him. With the flow of souls restored in Hell, Satan regains his body and recommends that Nicky go back to Earth.

The film ends a year later, when Nicky and Valerie live in New York with their infant son Zachariah. It is mentioned that John and Peter have died in a plane crash and are now happily living in Hell in Nicky's old room.