Dentist Frank Sangster appears to have it all: a thriving practice shared with his beautiful girlfriend/dental hygienist Jean. But when new patient Susan Ivey seeks his help, he's so attracted to her that he prescribes her powerful drugs against his good sense. He also lets his junkie brother Harlan stay with him, although Jean despises Harlan.
Susan seduces Frank--naughty, naughty--in the dental chair. Worse, he later finds that all the drugs in his clinic have been stolen. Frank covers up the theft from Jean and the authorities but demands the drugs back from Susan. But she and her hot-tempered, incestuous brother and fellow junkie Duane have gone through them.
Duane visits the clinic and warns Frank to stay away from Susan. Frank goes to see Susan but gets into a fight with Duane instead. Frank goes home and finds Duane dead. Jean shows up and makes panicky Frank call the cops. Frank lies about his relationship with Susan to Detective Lunt and Hollywood star Lance Phelps, who's researching an upcoming movie role. But Jean finds out about his affair with Susan and is hurt.
Frank goes to Susan's motel but sees her with Harlan. Harlan tells Susan that Frank killed Duane. Frank denies killing Duane and so does she. Susan tells Frank that Harlan got her to seduce Frank and steal his drugs. The police arrest Frank for Duane's murder after his teethmarks are found all over Duane's body. But Frank escapes with the unwitting help of Lance Phelps.
Frank convinces Susan to help him. At Jean's house, they find dentures of his teeth. Frank learns that Jean will take over their dental practice if he's convicted of murder. They overhear her talking on the phone and asking her co-conspirator to plant the weapon used to murder Duane in Frank's clinic.
At the clinic, Harlan shows up with the shotgun Jean used on Duane. They argue because Harlan didn't want Jean to kill Duane. Jean kills Harlan. Frank arrives too late and finds Harlan's dead body covered with his teethmarks. Backed into a corner, Frank extracts all Harlan's teeth and then all his own. He replaces Harlan's teeth with his own and sets fire to the clinic.
In the ashes, the only remains are of Frank's teeth. The cops presume Frank dead and find a videotape of Jean confessing to the murder that had been secretly recorded by Harlan and stored in a fireproof safe. Jean is sentenced for the murders of Duane and Frank. Frank writes a book, Novocaine, using Harlan's name and retires to a villa in France with Susan.