On a rainy New England night in 1954, a butler named Wadsworth readies the Hill House estate for a dinner party. As the guests arrive, Wadsworth assigns them aliases to use for the evening, and instructs them not to use their real names. Over dinner, the guests, Mrs. Peacock, Colonel Mustard, Mrs. White, Mr. Green, Professor Plum, Miss Scarlet, and Mr. Boddy learn they all live or work in Washington, D.C., and demand to know why they are there, as they have all received a mysterious invitation requesting their attendance. In the study, Wadsworth, also unaware of the party’s host, reads a letter instructing him to explain the guests’ presence. As Mr. Boddy grows tired of the mystery and attempts to leave, he finds that all the doors and windows are locked, and the house is surrounded by attack dogs. Back in the study, Wadsworth shares that all the guests have secrets and that they have all been blackmailed by an unknown person. The letter instructs the butler to shed light on the partygoers’ secrets, and includes evidence of their misdeeds ranging from bribery, prostitution, and immoral conduct. Curious to learn Mr. Boddy’s secret, Wadsworth names him as the guests’s blackmailer, and reports that the police will arrive in forty-five minutes to arrest him. However, Mr. Boddy claims he has evidence that will keep them silent about his blackmailing scheme. Giving each of the guests a wrapped box, Mr. Boddy explains his letter from the unknown host revealed who would be in attendance. As the boxes are opened to reveal a candlestick, a rope, a lead pipe, a wrench, a revolver, and a knife, Mr. Boddy suggests that one of the guests should use their weapon to kill Wadsworth, since he holds the keys to the doors, and knows all of their secrets. Mr. Boddy shuts off the lights to create an opportunity for the murder. In the darkness, a thud is heard, and a gun is fired. When the lights are turned on, Mr. Boddy lies dead. As there is no gunshot wound, the guests try to determine who the murderer is, and what weapon was used. Elsewhere in the manor, Yvette, the maid, screams, and when the others find her, she admits to hearing everything, and is terrified of the murderer. Wadsworth later reveals that he was the one who sent the letters, as he had also been blackmailed by Mr. Boddy when he worked for him as a butler. Learning of Wadsworth’s wife’s socialist associations, Mr. Boddy enslaved the couple. In turn, they could not pay him off, and it prompted the suicide of Wadsworth’s wife. Wadsworth planned the evening so Mr. Boddy’s victims could confront him, and have him arrested. As the guests accuse each other of Mr. Boddy’s murder, they discover the cook has also been killed. Back in the study, the body of Mr. Boddy disappears, then turns up in the hallway, making it unclear where the murder occurred. Later, a motorist with a broken down car comes to the door to use the telephone, and the guests worry he will see the dead bodies, so Wadsworth locks him in the lounge while he makes his phone call. Fearing there is someone else in the house committing the murders, the guests split into pairs to search the manor. Meanwhile, an unseen figure destroys the evidence, then sneaks into the lounge and murders the motorist, just as he admits over the telephone to recognizing one of the party goers as his former boss. Discovering a secret passage, Miss Scarlet and Colonel Mustard enter the lounge, and find the slain motorist. Later, a policeman arrives, searching for the owner of the broken down car, and when he asks to use the telephone, his suspicions are aroused by the anxious guests. When someone cuts the power and shuts off the lights, Yvette and the policeman are murdered, along with a woman who came to the door as a singing telegram. Wadsworth claims to know who the murderer is, and replays the night’s events outloud, revealing that the motorist, the policeman, and the singing telegram woman were all Mr. Boddy’s accomplices, and not there by chance. Wadsworth accuses Yvette of the first few murders, and, suggesting that Miss Scarlet was her employer, accuses her of the remaining killings. Miss Scarlet pulls the revolver from her purse and confesses to stealing her fellow partygoers’ secrets, then threatens them to keep quiet about the murders. Noting that Wadsworth has no secrets for which to be silenced, Miss Scarlet prepares to shoot him, but he declares she is out of bullets. Before she can challenge his attentions, the police arrive and arrest her. However, another ending is suggested with Mrs. Peacock as the guilty party. As a ruse, Wadsworth does not have her arrested, claiming he approves of Mr. Boddy’s murder, while outside, the Federal Bureau of Investigations (FBI) awaits to arrest her. In a third scenario, the truth is at last revealed, that each guest is guilty of one of the night’s murders. Wadsworth admits he is the real Mr. Boddy, and suggests they depart without involving the police. Mr. Green refuses to allow the blackmailing to continue, and shoots Wadsworth. Revealing that he is an FBI agent, Mr. Green opens the door for his awaiting men, and has the murdering guests arrested.