In Morocco, Frank Cotton, a hedonist with an insatiable appetite for sensation, buys a mysterious puzzle box said to open the door to a realm of otherworldly pleasure. Back in his bare attic, he solves the box and hooked chains emerge, tearing him apart. A black-robed figure resets the puzzle and the room is restored to normal.
Later, Frank's brother Larry moves into the same house. He intends to rebuild his relationship with his second wife, Julia. Larry is unaware that Julia had an affair with Frank before her marriage to him. When Larry accidentally cuts his hand moving furniture, his blood drips on the attic floor and resurrects Frank in a ghastly form. Julia later finds Frank; still obsessed with him, she agrees to help restore his body, so they can run away together. Julia picks up men in bars and brings them back to the attic, where she mortally wounds them. Frank then drains their life, which regenerates his body. Frank explains to Julia that, having exhausted all sensory experiences, he sought out the puzzle box, which was supposed to provide access to a realm of new carnal pleasures. When the puzzle was solved, the Cenobites came to subject him to extreme sadomasochism.
Kirsty, Larry's teenage daughter and Frank's niece, sees Julia bringing a man to the house and follows her to the attic, where she finds Frank. She evades Frank and escapes with the puzzle box, collapsing shortly thereafter. Awakening in a hospital, Kirsty solves the box out of curiosity, and unknowingly summons the Cenobites and a monster called the Engineer, from which she narrowly escapes. The Cenobites' leader explains that although they have been perceived as both angels and demons, they are simply "explorers" from another dimension seeking carnal experiences, and they can no longer differentiate between pain and pleasure. When they attempt to force Kirsty to return to their realm with them, she informs Pinhead that Frank has escaped them. The Cenobites agree to spare Kirsty and recapture Frank instead, with the condition that Frank must confess to escaping them.
Kirsty returns home, where Frank has killed Larry and has taken on his identity by wearing his skin. Julia shows her what is purported to be Frank's flayed corpse in the attic. Julia then leaves the attic, locking the door behind her. The Cenobites appear and, not fooled by the deception, demand the man who "did this." Kirsty tries to escape, but is held by Julia and Frank. Frank reveals his true identity to Kirsty and, when his sexual advances are rejected, he decides to kill her to complete his rejuvenation. He accidentally stabs Julia instead and drains her without remorse. Frank chases Kirsty to the attic and, when he is about to kill her, the Cenobites appear after hearing him confess to killing her father. Now certain he is the one they are looking for, they ensnare him with chains with hooks and tear him to pieces. When the Cenobites double-cross Kirsty and attempt to take her, she grabs the puzzle box from Julia's dead hands and banishes them by reversing the motions needed to open the puzzle box. Kirsty's boyfriend Steve Martin arrives and they both escape the collapsing house.
Afterwards, Kirsty throws the puzzle box onto a burning pyre. A vagrant who has been stalking Kirsty walks into the fire and retrieves the box before transforming into a winged skeletal creature and flying away. The box ends up with the same merchant who sold it to Frank, where he offers it to another customer.
