A man who has been railroaded into prison is framed for the murder of a fellow inmate and must prove his innocence.

A private detective, soon to enlist in the army, is drawn into one final case when his police officer father is killed in the line of duty. Soon his prime suspect is murdered as well, and he finds himself framed for the crime. As more witnesses get murdered, he finds himself on the run from both the police and former Prohibition violators who seem to have found a new racket.

After Police Captain Dan McLaren becomes police commissioner, former detective Johnny Blake publicly punches him, convincing rackets boss Al Kruger that Blake is sincere in his effort to join the mob. "Bugs" Fenner, meanwhile, is certain that Blake is a police agent.