Sid Brady, the chief of police detectives, arrests gangster Rudolph Spain for murder on the day that the criminal marries Muriel Vance. Because Muriel had recently jilted Sid to marry Spain, the arrest generates malicious gossip regarding the detective's motives. When Spain is sprung from jail immediately following his arrest, Sid becomes suspicious. Sid's suspicions intensify when his right-hand man, Jimmy March, is run down by a taxi after he undertakes an investigation of the crooked fight rackets and related death of boxer Tiger Renoir. The accident was really a murder attempt on Jimmy's life, and when Jimmy survives the mishap, he visits Spain and announces that he can identify Tiger's murderer. As Jimmy threatens Spain, the gangster receives a phone call from the chief of the crime ring, ordering Jimmy's execution. Riki, Tiger's twin brother and Spain's valet, overhears the call, and Jimmy is killed. When Muriel realizes that her husband is a murderer, she tries to leave him, but he knocks her unconscious. Soon afterward, Sid appears and forces a confession from Spain, but when the gangster pulls Muriel's gun on him, Sid is forced to shoot him in the line of duty. Spain's confession convinces Sid that there is someone in a powerful position involved with the gangster, and he enlists Riki's aid in identifying the voice that he heard over the phone. Returning to the station house, Sid keeps silent about the shooting and is assigned to Spain's murder case. Finding Muriel's fingerprints on the gun, Sid accuses her of murder, and after ordering her arrest, he notifies police commissioner Cromwell that the arrest is really a set-up to coerce Muriel into revealing who the power is behind Spain. After Spain's lawyer arranges for Muriel's release from jail, she visits Cromwell and asks for his protection. When Cromwell pulls a gun on Muriel and announces that he ordered Jimmy's execution, Sid springs from the next room to arrest the chief of the crime ring.