Following the Hillsdale Express train robbery in which a million dollars was stolen and a mail clerk was killed, 'Tough' Tommy Karpeles is convicted and sentenced to life in prison. Eliot Ness has been tasked by the Post Office to recover the missing million and he begins to think that Karpeles may be innocent. Information from a dying hood puts him on the trail of Karpeles' former associate Arnie 'The Wolf' Mendoza, now a supposedly reformed cinema owner living under the name of Albert Maris.