The Dentist

On his wedding anniversary, Dr. Alan Feinstone finds out that his wife Brooke is cheating on him with the poolman, Matt. This revelation triggers his obsessive-compulsive disorder and begins his descent into instability. Alan's obsession with perfection and cleanliness is contrasted with the emotional betrayal he feels.

After confronting the betrayal, Alan retrieves his pistol and follows Matt in his car, leading him to Paula Roberts's house, a friend of Brooke. Alan fabricates a story about a surprise party to maintain his cover while observing the scene. Paula's dog attacks Alan, prompting him to shoot it in self-defense.

Back at his dental office, Alan starts his day with a client who hallucinates about rotten teeth. An incident occurs where Alan accidentally stabs the child patient, revealing his fragile mental state. The day is marked by increasing tension and hallucinations that influence his actions.

Alan hallucinates that April Reign, a beauty queen patient, is his wife. While she is unconscious, he unbuttons her and attempts to strangle her, but snaps out of his hallucination when she wakes. His mental instability grows, leading to aggressive behavior in the clinic.

Later that night, Brooke arrives at Alan’s office, where he sedates her under the pretext of a cleaning. Once unconscious, Alan gruesomely pulls out her teeth and cuts off her tongue, intensifying his disturbing behavior.

Detectives Gibbs and Sunshine arrive at the house and question Alan about Paula's dog's death. Their investigation reveals the dog’s bullet matches Alan's gun. The detectives then find Brooke alive but sedated and later discover that Alan has murdered Matt.

Alan's assistant Jessica questions his behavior during a session, and when she threatens to expose his crimes by revealing April's pantyhose, Alan kills her in a violent outburst. This marks a turning point towards his complete descent into madness.

Detective Sunshine uncovers that Alan’s gun matches the one used in Paula’s dog’s death. Alan tortures IRS agent Marvin Goldblum and later murders his assistant Karen after attacking her. His killing spree continues as he aims to cover his crimes, demonstrating his growing brutality.

After removing Sarah’s braces, Alan hallucinates her teeth rotting and attempts to kill her, but she escapes and hides. Alan's violence culminates in a confrontation at a university where he instructs students to pull teeth and shoots a fellow student in his hallucination, further demonstrating his break from reality.

Alan wanders into an auditorium where he sees a performer he believes is Brooke, who mocks him, leading him to collapse. The detectives arrive, arrest him, and he is taken to a psychiatric hospital, signifying the end of his murderous rampage and mental breakdown.

In the concluding scene, Alan undergoes dental treatment at the hospital, only to find that the dentist working on him is his wife Brooke, now toothless and working violently, symbolizing the cycle of his obsession and madness.