Gang leader Cody Jarrett (James Cagney) lives for his mother, planning heists between horrible headaches. During a train robbery that goes wrong, Cody shoots an investigator. Realizing Cody will never be stopped if he knows he's being pursued, authorities plant undercover agent Hank (Edmond O'Brien) in Cody's cell. When his mother dies, a distraught Cody breaks out of jail, bringing Hank along to join his gang. With Hank in communication with the police, Cody plans a payroll heist.