Billy Halleck (Robert John Burke) commits vehicular homicide when his lack of attention to driving results in the death of an old gypsy lady on the street. Overweight Halleck is a lawyer with connections, though, and gets off with a slap on the wrist. After his trial, the woman's husband, Tadzu Lempke (Michael Constantine), curses him with a single word, “Thinner.” Halleck begins to lose weight uncontrollably and must pursue the band of gypsies who are responsible for his dwindling condition. He enlists the aid of one of his clients, gangster Richie Ginelli (Joe Mantegna), to scare the woman's family away from their harrassment of him.