As a jazz quintette plays their last night at Vic's Café in Los Angeles, having been offered a better job in San Francisco, Anita Lane, their conniving female vocalist, threatens to break up the engagement of Danny, the trumpeter, to Jean, a schoolteacher, unless she is allowed stay with the band. Upon the conclusion of their last set, Johnny, the band's drummer who is in love with Anita, drunkenly wanders backstage and passes out. Soon thereafter, the band finds Anita murdered in the same room, but Danny, who served in the Navy with Johnny, insists that they say nothing, as he is afraid that Johnny will be accused of the crime. Police detective Roger Quinn, a jazz connoisseur, is assigned the case and quickly tracks the band to San Francisco, where he identifies Danny by his trumpet playing. Rather than arresting Danny, Quinn pretends to be an investor interested in putting a band together. Johnny falls for the bait and places a classified ad in a San Francisco paper calling the band back together, but when he and Danny go to Quinn's hotel room, they recognize their recording of "China Boy" and realize that he is a policeman. Yet to be arrested by Quinn, the two then go back to Los Angeles, as Danny thinks he can clear the band. The band is captured by Quinn, however, as they meet backstage at Vic's. Danny is accused of the murder, as he was heard fighting with the singer by Pete, a waiter, and his trumpet has an unexplained dent in it. Meanwhile, Vic Miller, the nightclub's owner, tries to convince Jean that Danny was having an affair with Anita, but she soon realizes that he is the real killer. Just in time, Quinn stops Vic from killing Jean, and Vic then is captured by Danny and the band as he attempts to escape. Later, Vic confesses that he killed Anita out of jealousy, as she wanted to leave him for the band. With his name cleared, Danny is reunited with Jean and the two make plans for their wedding.
