After ruling Hell for the past ten thousand years, the Devil (HARVEY KEITEL) must choose which of his three sons will take his place on Hades' throne. Either Adrian (RHYS IFANS) or Cassius (TOMMY "TINY" LISTER JR.) seem the most likely choices since they're certainly evil, with meek Nicky (ADAM SANDLER) having no chance due to his weak and less than evil nature.
When the Devil decides to continue ruling rather than appoint one of his sons, Adrian and Cassius are outraged and set out for Earth where they'll convert enough souls into supporting them that they'll be able to overthrow their father. Passing through the gates of Hell and overcoming the Gatekeeper's (KEVIN NEALON) attempts at stopping them, the rebellious sons' actions freeze the gates and set into motion the slow, disintegrating death of the Devil.
Prompted by the Devil's assistant, Jimmy the Demon (BLAKE CLARK), his grandfather, Lucifer (RODNEY DANGERFIELD) and the desire to save his dad, Nicky agrees to travel to Earth for the first time to return his errant siblings. Armed with a magic flask that will capture them should they fooled into drinking from it, Nicky arrives up top with no knowledge of how anything works there.
After being accidentally killed and returned to Hell, Nicky is sent back to Earth where's he then accompanied by Beefy (voice of ROBERT SMIGEL), a talking dog and old friend of the Devil's. Showing Nicky the ropes, Beefy helps him track down the brothers and sets him up with a roommate,
Todd (ALLEN COVERT), who's presumably in denial of his own homosexuality.
As Nicky tries to find and channel the evil within him to battle and then capture his brothers who can possess people and thus look like others, he meets and falls for fashion student, Valerie (PATRICIA ARQUETTE), while being aided by heavy metal Devil worshippers, Pete (PETER DANTE) and John (JONATHAN LOUGHRAN). With less than a week before his father disappears and Adrian takes over, Nicky does what he can to stop that from happening.