Johnny Morrison returns home from the war to find out his wife is having an affair with Eddie Harwood. The Morrisons argue and Johnny leaves, only to be picked up by an attractive mysterious woman. Mrs. Morrison asks Johnny's soldier friends Buzz and George to bring him home. Buzz's war wound have made him short-tempered and violent, but he goes to Mrs. Morrison's hotel home. She's also visited by her lover and nightclub owner Eddie Harwood, who tries to end the affair but whom she threatens. Keeping a watchful eye is the house detective.
When Mrs. Morrison is murdered, Johnny is the prime suspect. Johnny eludes the police manhunt and confronts Eddie, who has just bribed the house detective to keep quiet about Eddie's visit to the Morrison residence the night of the murder. Johnny learns that the mysterious woman who picked him up is Eddie's estranged wife, Joyce. Johnny is kidnapped by Eddie's men, but in the ensuing struggle, one of the henchmen kills Eddie.
Johnny goes to the Blue Dahlia, where the police are questioning Buzz and George and the house detective Newell. Buzz becomes hysterical at the sight of Joyce plucking blue dahlia petals. He had also been hysterical when he saw Mrs. Morrison pluck dahlia petals. Although Buzz seems to be the killer, he claims he ran away from Mrs. Morrison. The cops trick Newell, who confesses to having killed Mrs. Morrison when she wouldn't give in to his attempts to blackmail her about her extramarital affair with Harwood.
Johnny and Joyce leave together.