After a witness is shot and a suspect hanged in a jail cell, Police Chief Sprague decides to send Sgt. Joe Geary undercover, looking for a mysterious crime-syndicate boss responsible for ordering these murders. A story is planted by the chief that Geary is being suspended from the force, in order to help him infiltrate the mob.
Geary discovers that a police captain is the criminal mastermind. Sprague is killed, though, and Geary framed when nobody believes his story about being undercover. While jailed, his fiancée Alice Devlin works to clear his name. Geary breaks out of jail and personally goes to the reform-minded governor to prove his innocence.