While driving alone in the Mojave Desert, Sandra Thomas's (Plummer) car breaks down after a road rage incident with another driver, Santini (Thewlis), who is later revealed to be a notorious scam artist.

Sandra is offered a lift by soft-spoken passerby Jake Nyman (Forster), who identifies himself as a Los Angeles psychiatrist on a pleasure trip with decisions based on a flip of a coin.

Sheriff Frank (Paul Sorvino) and Deputy Sam (Chris Sarandon) don't suspect Jake of wrongdoing based on his clean record and demeanor; the immediate implication is that Santini, a fugitive, was involved in Rita's death and Sandra's disappearance.

Concurrently, Jake incriminates himself to Alice as the psychopathic murderer of her sister, coldly reciting their childhood memories and showing Sandra's mutilated corpse in the trunk of his car.

As a last ditch effort to save her life and appease Jake's philosophy, Alice proposes a coin toss in which she can either walk free (heads) or he'll kill her (tails), using a switched double-headed Kennedy half dollar taken from Santini.