Upon the murder of an anti-crime advocate, the police turn to former investigating detective Johnny Blake (Edward G. Robinson) for help. Convinced that racketeer Al Kruger (Barton MacLane) arranged the murder, Johnny goes undercover in order to infiltrate Kruger's gang. Using his unsuspecting friend Lee Morgan (Joan Blondell), who runs a numbers racket, Johnny burrows into Kruger's organization while staying one step ahead of suspicious henchman Bugs Fenner (Humphrey Bogart).