Bill Anderson, a serial murderer known as "The Gemini Killer" who also suffers from multiple personality disorder, tortures captive Allison Perry in his basement using a blowtorch.Kelly Owen asks her wealthy musician husband Craig to pick up champagne. Outside the liquor store, Bill abducts Craig in a van advertising children's entertainer "Baylee the Clown."Craig wakes up tied to a school desk in Bill's basement. In his Baylee persona, Bill begins inflicting pain on Craig while strangely referring to Craig as Bill.Bill reappears as a police officer imagining he is arresting Craig for the Gemini killings. Bill also assumes the identity of an interrogating detective who smashes out Craig's front teeth with a handgun and forces Craig to eat them.Seemingly worried when he doesn't come home, Kelly drives to the liquor store to ask cashier Lauren if she knows what happened to Craig. Kelly also calls the police, but is told she must wait 24 hours before they can investigate. Finally, Kelly calls her best friend Bianca, who comes to the house and spends all night in conversation with Kelly.Craig connects that Gemini kidnapped him and Bill is projecting his murderer identity onto Craig. Craig begins role-playing with Bill in an attempt to escape.While portraying a San Quentin convict supposedly imprisoned alongside Craig, Bill tells a story about he and his sister Marybeth being abused as children. Craig tries to relate by telling Bill that his wife was also abused when she was a foster child. Bill becomes angry and uses wire cutters to sever three of Craig's fingers.As Dr. Jack Goodman, Bill painfully sews up Craig's wounded hand. Bill tells Craig another story about being in a foster home with his sister.Bill reappears as a lawyer representing Craig prior to his execution. Craig unsuccessfully attempts to relate to Bill using an anecdote about losing his identity as a musician.Craig tries using the story about Marybeth to guilt Bill when he takes the identity of Bill's welder father visiting him on Death Row. Bill ends up briefly strangling Craig with a phone cord.Bill returns as his mother. Craig appeals to the personality for help escaping. Bill slips Craig a metal nail file.Bill next takes the personality of a prison guard. Deliveryman Andre arrives at the door with pizza for Craig's last meal, which Bill eats with Craig. Craig asks Bill about his Gemini tattoo. Bill tells Craig he has a twin.Craig uses the nail file to break free from his rope restraints while Bill is out of the room. Bill finds Craig trying to escape and recaptures him.Craig and Bill have another confrontation while Bill embodies Catholic priest Father Fitzgerald. When Craig offends him, Bill slices Craig's face with the nail file.Bill takes the persona of an executioner wearing the Gemini symbol. Over Craig's pleas, Bill uses his blowtorch on Craig's neck until he is able to tear off Craig's head.After sunrise, Bill comes to Kelly's house in his police officer uniform. Bill tells Kelly, "it's done." Kelly implies that she wants Bill to kill Bianca, who is still sleeping on her couch.One Month Earlier - Having deduced that her twin brother is The Gemini Killer, Kelly manipulates Bill into making Craig his next victim for cheating on her with Bianca.