In San Francisco, former private detective Nick Charles enjoys a peaceful retirement with his attractive wife Nora, their young son Nick, Jr., and their wire-haired terrier, Asta. One afternoon, when Nick and Nora go to the races, they learn from Nick's old friend, Lieutenant Abrams, that a jockey named Gomez has just been fatally shot. In the jockey room, Nick's police and reporter friends think that he is on the case, but he insists that his detective days are over, even when one of the jockeys piques his curiousity by saying that Gomez was killed because he refused to throw a race. That night, Major Jason I. Sculley, head of the State Athletic Commission, and investigative reporter Paul Clarke arrive at the Charles apartment, seeking Nick's help, but he again refuses, saying that he has promised to take Nora to a wrestling match. Later, at the arena, "Whitey" Barrow, a reporter and rival of Paul, blackmails suspected racketeer "Link" Stephens' girl friend, Claire Porter, into giving him her diamond bracelet. While Nick and Nora watch the match, bookie "Rainbow" Benny Loomis goes to Stephens' office upstairs and hides when Whitey comes in and demands money for keeping Stephens' name "clean" in the newspapers. After Whitey leaves, Benny angrily tells Stephens that Whitey owes him $8,000. In a nearby restaurant, Paul meets his girl friend, Molly Ford, who has been helping his investigation by working undercover as Stephens' secretary, and she reluctantly gives Paul her office key. As Paul searches Stephens' office, he is confronted by a gun-wielding Whitey, who demands a notebook that Paul has just found. During a scuffle, Whitey takes the notebook and knocks Paul out. Then, an unseen assailant shoots Whitey, just as a night watchman sees Benny going down the stairs. After the match, Nick and Nora again run into Abrams, who tells them about Whitey's murder. In Stephens' office, as a dazed Paul is questioned by police, Nora asks Nick to do something to help. Nick quickly determines that a piece of paper lying on the floor is a tally for a bookie operation, and Paul is arrested by Abrams. Nick then goes with Asta to the racetrack to search the jockey room and discovers that in a freakish accident, Gomez killed himself. The next day, however, Nick goes to Abrams and tricks him into releasing information to the press, saying that the police are convinced that Gomez and Whitey were killed by the same person and that an innocent Paul is being released. Following a hunch, Nick goes to visit Claire, who says she hardly knew Whitey, but her anger makes Nick suspicious. Nick then goes to Whitey's apartment, where Asta helps him find a diamond bracelet. Just then, Claire enters the apartment and Nick hides while observing her search for something. He then confronts her and she admits that the bracelet is hers and that although Whitey blackmailed her, she does not think that Stephens knows that she had once been Whitey's girl. She also tells Nick about the money Whitey owed Benny. That night, Nick and Nora meet Paul and Molly at a restaurant, where Nick runs into Benny and tells him that the watchman saw him the night of Whitey's murder. Benny nervously leaves after Nick discovers that he is wearing a bullet-proof vest. Paul then calls Sculley and says that Nick needs information, and Sculley agrees to meet them at Benny's apartment building. Sculley, who says that he had talked to Benny a few days before, takes them directly to Benny's apartment, where they find his hanging dead body. They also find remnants of the notebook and Nick observes that the rough markings on Benny's neck rule out a suicide. Nick then suggests that all of the suspects be assembled in Abrams' office. The next day, Nick confronts each suspect with reasons why he or she might be the murderer and solves the case when the superintendent of Benny's building calls to say that Benny had only lived for three hours in the apartment in which he died. Because Sculley took Nick and Paul right to Benny's place, Nick deduces that Sculley killed Whitey then Benny to cover up the fact that Stephens had been bribing him. Sculley then grabs Nick's gun, but Nora jumps him and saves everyone, unaware that Nick had earlier emptied his gun.