The film follows Billy Halleck (played by Robert John Burke), a morbidly obese lawyer who accidentally kills an old Romani woman named Suzanne Lempke (played by Irène Jacob) with his car. Despite the incident being witnessed by several people, Billy is acquitted due to his connections and influence in the town.
However, Billy soon begins to experience strange and terrifying phenomena. He starts losing weight rapidly, despite not changing his diet or lifestyle. As his weight continues to plummet, Billy becomes increasingly desperate to find a cure for his mysterious illness.
Billy eventually learns that Suzanne’s father, Tadzu Lempke (played by Michael Constantine), is a powerful Romani patriarch who has placed a curse on him as revenge for his daughter’s death. Tadzu warns Billy that the curse will continue until he returns the favor by taking someone else’s life.
Desperate to lift the curse and save himself, Billy enlists the help of his friend and colleague, Dr. Mike Houston (played by Joe Mantegna), to find a solution. Together, they embark on a dangerous journey to confront Tadzu and break the curse before it’s too late.
As Billy’s condition worsens, he becomes consumed by guilt and paranoia. He begins to suspect everyone around him, including his own wife, Heidi (played by Lucinda Jenney), and their daughter, Linda (played by Kari Wuhrer), of plotting against him.
In the film’s climax, Billy confronts Tadzu and attempts to reason with him, but Tadzu refuses to lift the curse. Desperate and running out of time, Billy takes matters into his own hands and seeks revenge on those he believes are responsible for his predicament.
In the end, Billy’s obsession with revenge leads to his downfall. He inadvertently kills the wrong person, triggering a chain of events that ultimately culminates in his own demise. As he dies, Billy finally realizes the true cost of his actions and the futility of seeking vengeance.
“Thinner” is praised for its atmospheric tension, compelling performances, and exploration of themes such as guilt, morality, and the consequences of one’s actions. It remains a chilling and thought-provoking horror film that leaves a lasting impression on viewers.