A fat Lawyer finds himself growing "Thinner" when an old gypsy man places a hex on him. Now the lawyer must call upon his friends in organized crime to help him persuade the gypsy to lift the curse. Time is running out for the desperate lawyer as he draws closer to his own death, and grows ever thinner.
When a gypsy caravan arrives in Fairview, the judge Phillips forces the gypsies to leave town. Meanwhile the gluttony lawyer Billy Halleck, who has difficulties to reduce his weight, successfully defends the mobster Ritchie Ginelli in court. During the night, he celebrates with his partner and wives at a dinner party. While driving back home, his wife Heidi pleasures Billy during which he accidentally runs over the old gypsy Suzanne Lempke, the daughter of the patriarch Tadzu Lempke. During the trial, Billy omits the reason of the accident; the chief of police Duncan Hopley perjuries; and the bigoted judge declares Billy not-guilty. The next day, Billy, Duncan and Phillips are cursed by Tadzu, who puts a hex on each one of them. Billy gets thinner and thinner and while seeking out Tadzu to ask him to remove the spell, he suspects that his wife is having an affair with his doctor and friend Mike Houston. Billy feels that his life is running out and asks for help to Ritchie to convince Tadzu using his method to call off the jinx.
An obese attorney is cursed by a gypsy to rapidly and uncontrollably lose weight.
- Billy Halleck (Robert John Burke) is an arrogant, obese, upper-class lawyer living in the suburban small town of Castle Rock, Maine with his 14-year-old daughter Linda (Bethany Joy Lenz) and his wife Heidi (Lucinda Jenney). After defending an underworld crime boss named Richie "The Hammer" Ginelli (Joe Mantegna) in court, the town is in the middle of a carnival which is run by Gypsies. One evening, he accidentally runs over an old Gypsy woman with his car when Heidi distracts him by performing oral sex on him. After a court hearing where Billy is cleared of any charges, the Gypsy woman's father, a 106-year old warlock named Tadzu Lempke (Michael Constantine) curses Billy by touching his face and saying the word "Thinner" before he and the Gypsy group leave town.
The curse causes Billy to lose weight rapidly, regardless of how much he eats. The old man also curses the corrupt Judge Cary Rossington (John Horton) and Police Chief Duncan Hopely (Daniel von Vargan) who helped Billy avoid punishment for the Gypsy woman's death. Later, Billy sees Judge Cary Rossington slowly turning into a lizard and after a hostile encounter with his wife, Rossington commits suicide. Duncan Hopely becomes mutated with over-sized pimples and he also commits suicide.
Billy continues to remain in denial to what is happening, but after visiting a clinic and finding his sudden weight loss inexplicable, he finally realises that the Gypsy curse is real. Because only Lempke can remove the curse, Billy must track down and persuade the ancient Gypsy man to lift the curse. He flees from his family when they disbelieve the curse and insist he seek psychiatric help.
Billy finally tracks down the Gypsy troupe at the carnival in the next town in Connecticut. But Lempke is unmoved and has his great-granddaughter Gina (Kari Wührer) shoot Cary's car window, who has picked Billy up. They then drive straight into a truck which is seemingly driven by Lempke. The experience turns out to be a nightmare that Billy experiences and learns that the Gypsy caravan has moved to the next town, where he confronts them. Gina then shoots him in the hand with her catapult, and christens him the "white man from town".
As his family grows frantic about his whereabouts, Billy enlists the help of Richie who believes in Gypsy curses and agrees to help him out. Richie pays an associate to track down the Gypsies for him. Richie kills off the camp dogs with poison and leaves a note saying "WHITE MAN FROM TOWN SAYS TAKE IT OFF." But the next day, the Gypsies find the man who tracked them down and kill him and vandalize Billy's car.
The next evening, Richie turns up the heat and launches a one-man attack against against the Gypsy camp by firing off various automatic weapons at the camp trailers and he kills one Gypsy at the camp, who is Gina's husband. The next morning, Richie turns up at the camp impersonating "Agent Stoner" from the FBI where he lures Gina away from the group to a old barn where he confronts and brutalizes her in order to persuade Lempke to lift the curse. Billy stops Richie from killing her. Richie threatens Gina with acid and gives her a message for her great-grandfather: meet them at the lighthouse in two hours. Richie then drops off Billy at the meeting place and drives off.
Lempke arrives at the meeting, convinced that only by lifting the curse can he prevent further attacks on his people. He explains to Billy that he cannot remove the curse, but it can be transferred to another victim. Lempke then performs this by stabbing Billy in his wounded hand and mixing his blood with a strawberry pie that he has brought with him. Lempke tells Billy that the curse will be lifted for a short while, but the cursed pie must be consumed by an unsuspecting person, causing painful but rapid death or the curse will return. Lempke urges Billy to end the curse and commit suicide with dignity by eating the pie himself.
Billy returns home to Castle Rock with the pie, but he believes that his wife Heidi has been cheating on him during his ordeal, so he leaves the pie out in the kitchen for her to eat.
The next morning, he wakes up to find Heidi's disfigured corpse next to him in bed. Initially gleeful to be free of the curse and of his disloyal wife... he finds to his horror that Linda has also just eaten a slice of the cursed pie and that she will die very soon as well.... thus Billy realizes that Lempke has gotten his final, back-at-you, revenge for all this. Billy also reads an article from the morning newspaper that Richie was found dead in New York City under mysterious circumstances... implying that he may have been murdered by the Gypsies.
Billy's guilt compels him to "die with dignity" and ends up having to take Lempke's offer to eat a piece as well. Before he can do so, a local doctor (whom he suspects to be his wife's adulterous lover) named Dr. Mike Houston (Sam Freed) arrives at the door. Dr. Mike Houston immediately suspects something is wrong and attempts to leave. However, Billy invites the man in to share the pie with him....