| Director | Jonathan Lynn |
|---|---|
| Budget | $15 million |
| Box office | $14.6 million |
In 1954, six strangers are invited to a secluded New England mansion. They are greeted by the butler Wadsworth and the maid Yvette. Each is assigned a pseudonym to maintain confidentiality: "Colonel Mustard", "Mrs. White", "Mrs. Peacock", "Mr. Green", "Professor Plum", and "Miss Scarlet". During dinner, they discover that they all have ties to the United States government, and are joined by a seventh guest, Mr. Boddy.
Wadsworth reveals that Boddy is responsible for blackmailing each guest by threatening to expose their un-American activities, such as murder, corruption, adultery, and homosexuality, and tells the guests that the police will soon arrive to arrest Boddy. Boddy proposes that the guests kill Wadsworth to avoid their secrets being revealed, and presents each with a weapon—a candlestick, rope, lead pipe, wrench, revolver, and dagger—before turning out the lights. After a gunshot rings out, Boddy is found apparently dead. Wadsworth confesses that Boddy had also blackmailed him over his wife's association with socialists. After she took her own life, he assembled the guests to convince them to testify against Boddy.
Suspecting the cook killed Boddy, the guests search for her and find her stabbed to death in the kitchen. Returning to the study, they discover Boddy is missing and conclude he is still alive, only to find him bludgeoned to death with the candlestick in the hallway. Wadsworth locks the weapons in a cupboard, but before he can dispose of the key, a stranded motorist arrives.
The group splits into pairs to search the mansion, but someone burns the blackmail evidence, unlocks the cupboard, and kills the motorist. Mustard and Scarlet discover a secret passage leading to the lounge, where they find the motorist's body. Their cries for help prompt Yvette to free them by shooting the locked door with the revolver. The group deduces that the murderer pickpocketed the cupboard key from Wadsworth.
A police officer investigating the motorist's abandoned car arrives to make a telephone call. After successfully distracting the officer and concealing the bodies, the group resumes its search, but someone cuts the electricity. In the darkness, Yvette, the officer, and an arriving singing telegram girl are murdered.
After restoring the power, Wadsworth gathers the guests and reconstructs the night's events, explaining that the victims were informants connected to each guest. Three endings are then presented.
In the first, Yvette is revealed to have murdered the cook and Boddy on Scarlet's behalf, while Scarlet killed the remaining victims, intending to replace Boddy as the group's blackmailer. In the second ending, Peacock is revealed to have committed all the murders to protect her secrets. In both endings, the police arrive to arrest the perpetrator, and Wadsworth is exposed as an undercover FBI agent.
The third ending reveals the truth: Peacock stabbed the cook (her former employee), Plum bludgeoned Boddy, Mustard killed the motorist (his former driver), White strangled Yvette (who had sex with her husband), Scarlet murdered the police officer (whom she was bribing), and Wadsworth shot the singing telegram girl (with whom Plum had an affair). Wadsworth then reveals that he is the real Boddy and that the man killed earlier was his butler. He orchestrated the murders to eliminate his informants and evidence of his crimes, but intends to continue blackmailing the guests. However, Green draws his own revolver and kills Wadsworth, revealing himself to be an undercover FBI agent. The police arrive and arrest the guests, while Green, who was believed to be homosexual, announces that he is going home to have sex with his wife.