Cleo, studying music at the conservatory and short of funds, is forced to give up her lessons. She returns home, and secures a position as singer with Follies Cabaret. In the meantime Jacques Fournier, a criminologist, is engaged in the solving of a murder mystery. Browne rushes to Fournier's office and tells him of the discovery of his wife's body. In investigating Fournier discovers that Browne is a cocaine fiend, and also that Mrs. Browne was killed by a Spiess gun. He learns that Browne has been associated closely with Audrey Devine, a singer at the Follies Cabaret. That night Fournier meets Cleo and saves her from the advances of Murphy, an Alderman. She tells him of her poverty and informs him that Audrey Devine, whom she has met in the dressing room, is addicted to cocaine. Fournier tells her to find out where she obtains the dope. Pretending that she, too, is a cocaine fiend, Cleo obtains the drug from Audrey who gets it from Max, the piano player. She informs Fournier that Max has the drug. In a note Fournier tells Cleo to play up to Max and have him take her home, and that he, Fournier, will hold them up and try to find out where Max obtains the drug. She follows his instructions and in the fight Fournier obtains Max's coat with the cocaine decks and the address, "16 Martin Street." The next morning, Cleo, in disguise, starts out for this address. Fournier has given her a powerful narcotic and skeleton keys, with instructions to substitute the narcotic for the cocaine. When Cleo reaches the hall at 16 Martin Street, Audrey is just leaving, but does not recognize the girl. Before this Audrey is shown inside the room with Max and Joe, another fiend, preparing the decks of cocaine. Audrey goes through a secret panel and gives decks to someone inside. When Cleo enters the room she finds it deserted and immediately starts substituting the narcotic. She also discovers the presence of a secret panel and is about to investigate when she is interrupted by the return of Joe. She tells him that she found the door open and merely peeked in. That night Fournier waits at the police station for orders from Cleo. Plain clothes men watch No. 16 Martin Street and see Audrey and Max enter the house. After the show Cleo goes directly to the police station and acts as guide to Fournier and the police. They surround the house and Cleo leads them to the door. They break in the door and find Max and Joe doped by the narcotic. Cleo tells them of the secret panel and they break in and find Audrey and Browne in each other's arms. Under a loose board Cleo discovers a Spiess gun and the dead woman's missing jewels. As Fournier revives Browne he holds the evidence in front of Browne's eyes, and Browne confesses to the murder of his wife. The criminals are arrested and Cleo becomes Fournier's partner.