Boston Blackie (Chester Morris) is a former burglar who has left his criminal past behind him. When a dead body is discovered in Blackie's apartment, he immediately becomes the chief murder suspect. In order to prove his innocence, Blackie begins his own investigation. With a well-intentioned police officer named Inspector Faraday (Richard Lane) close on his trail, Blackie eventually stumbles upon a circle of deadly secret agents masquerading as members of a Coney Island sideshow.