Late one foggy night, reporter Chris Williams saves Diana Leslie, a stranger, from drowning in the city river. Police investigator Reilly believes that Diana was attempting to kill herself, but Chris suspects that someone tried to murder her, and while the unconscious Diana rests in the hospital, he begins his own investigation into the mysterious drowning. In an interview with Diana's parents, Chris learns that their daughter's troubles began when she met Jimmie Lobo, a clarinet player at the Kitten Club, who tried to persuade Diana to pursue a career as a singer. Diana's mother then describes Jimmie's first visit to the Leslie house and the events that followed: After meeting her parents, Jimmie invites Diana to go with him to a "jam session" at the Kitten Club, but Diana's excessively protective brother Ted objects to the invitation and calls Jimmie and his pal "jive jumpers." Diana goes to the club, regardless, and returns later that night with news that she has taken a job there. Her family tries to persuade her to keep her office job, but Diana angrily opposes them, and Ted strikes her across the face. Diana's mother concludes her story by telling Chris that Diana left home that night and never returned. Jimmie later tells Chris that the first night he took her to the Kitten Club, Diana so impressed him with her singing, that he asked her to join his band. On the basis of his conversation with Jimmie, Chris concludes that Diana spurned Jimmie, and that he tried to kill her out of revenge. Chris then goes to the Kitten Club, where Steve Raymond, the crooked owner, recalls the day he first met Diana: While Raymond and his partner, Irene Mitchell, wait for Marien Mason, the band's alcoholic singer, to show up for rehearsals, Jimmie introduces them to Diana. Diana sings for Raymond and Irene, and they give her a job in the chorus. Raymond ends his story by telling Chris that Diana began her career as a naïve girl, but left the club with a "swelled head." Later, Chris, posing as Texan Henry Emerson, interviews Irene, who introduces him to Diana's roommate, Flo. The interview ends abruptly when Raymond finds Chris talking to Irene, but Flo follows Chris and tells him about the night she first met Diana: Moments after Flo warns Diana to get out of the club business before it is "too late," Irene introduces the two women to Ed Blake and Wilbur Harris, their "dates" for the night. Diana and Flo accompany Ed and Wilbur to the club's casino and encourage them to continue playing the roulette wheel until they lose all their money. When a shot rings out in the club and Wilbur is found dead, Raymond sees that Diana is frightened, and prevents her from talking by threatening her with harm. A short time later, Marien is replaced by Diana as the band's singer. When Diana tries to dissuade Flo's younger sister Alice from leaving her studies to take a job at the club, Raymond and Irene accuse her of interfering in their business. Flo comes out of her reverie and tells Chris that Diana told her that she intended to expose Irene and Raymond as racketeers. While Chris continues his investigation, his car is run off the road, and Flo is killed. Marien is later found murdered in her apartment, and her death is linked to Raymond's racket. Chris then discovers that Diana has been abducted from the hospital by Irene and Raymond, and taken to the Kitten Club. Chris and the police arrive at the club just as Irene is giving Diana a "sedative." Raymond confesses that he saw Irene follow Diana to the pier, and when Diana regains consciousness, she implicates Irene in the murder. Irene panics and shoots Raymond, but Jimmie kicks the gun out of her hand, and she is arrested.