Convicted on circumstantial evidence, Tommy Shay, a young product of the Front Street slums, is sentenced to die for the murder of police lieutenant Carson.
For his efforts, Lewis is demoted to patrolman, prompting his son Bob, a radio bug with an ambition to become a detective, to initiate his own investigation by which he hopes to find the real murderer and reinstate his father.
While searching for Collins on Front Street, Bob meets Danny and after he fibs that his father is a gangster, the boys join forces to track down Carson's killer.
In response, Foster begins to act strangely, giving the boys a look at his henchman, Halstead, whom they suspect is Collins.
Joining forces once again, the boys locate Halstead's hideout and lure Foster to the spot with a phony telegram.