Three discharged United States Navy officers, Johnny Morrison, Buzz Wanchek and George Copeland, arrive in Hollywood, California. Buzz is suffering from shell shock and has a metal plate in his head above his ear; George was released for bad eyesight; and Johnny was given leave after heroic actions in the South Pacific. Johnny surprises his wife Helen and discovers that she is having an affair with Eddie Harwood, owner of the Blue Dahlia nightclub on the Sunset Strip. Helen, drunk, confesses to Johnny that their son Dickie, whom Johnny believed died of diptheria, actually died in a car crash that occurred because she was driving drunk. Johnny pulls a gun on Helen, but drops it and leaves. Unaware of Helen's identity, Buzz goes to her bungalow for a drink. After Eddie ends the affair, Helen blackmails him into seeing her again. Johnny, meanwhile, is picked up in the rain by Joyce Harwood, who is separated from Eddie. Neither reveals their name, and they spend the night in separate rooms in a Malibu inn. The next morning, the radio announces that Helen has been murdered and that Johnny is suspected. "Dad" Newell, a house detective who saw Johnny fight with Helen and witnessed Buzz and Eddie enter her bungalow, goes to the police. Buzz and George are picked up for questioning, but Buzz remembers nothing. After Johnny checks into a cheap hotel under an assumed name, Corelli, the hotel manager, finds Johnny's photo of himself with Dickie and tries to blackmail him. Johnny beats Corelli up, then discovers that on the back of the photo, Helen has revealed that Eddie is really Bauer, a murderer wanted in New Jersey. Corelli revives and sells information on Johnny's identity to a gangster named Leo, who kidnaps him. Buzz and George visit Eddie at the Blue Dahlia, and Joyce introduces herself. As Joyce picks at a blue dahlia flower, the nightclub's music sets off a painful ring in Buzz's head, and lapsing into a fit, he remembers the agonizing music he heard while at Helen's bungalow as she played with a blue dahlia. Johnny escapes Leo's henchmen as Eddie arrives and forces him to admit that fifteen years before he was involved in the shooting of a bank messenger. Leo tries to shoot Johnny, but hits Eddie instead. Johnny flees to the Blue Dahlia, where the police are trying to force a confused Buzz to admit he killed Helen. Johnny enters and suggests that Joyce turn up the music. As his head pounds, Buzz remembers leaving Helen alive in her bungalow. Police Captain Henrickson then confronts Dad with the accusation that he he tried to blackmail Helen about her affair, and when she refused to comply, killed her. Dad then tries to escape from the office, but is shot by Henrickson. Later, outside the Blue Dahlia, Buzz and George decide to go for a drink, leaving Johnny and Joyce together.