Matt Bass is an ex-con and a former member of Al Capone's criminal empire. In prison, a fellow con, engineer Jason Fiddler develops what he thinks is the perfect way to deliver illicit liquor to central Chicago. Once out of jail, Bass approaches his old friend Frank Nitti to sell the idea. Nitti has been hit hard lately by Eliot Ness and the Untouchables who have pretty well shut down most of his distilleries and the speakeasies are starting to close their doors. Nitti tries to solve the delivery problem himself but in the end, agrees to Bass and Fiddler's scheme. Ness is soon on to them however.

Frank Nitti has a major problem: someone in his organization is leaking information to Eliot Ness and the Untouchables. They've closed down several of his distilleries and several members of the organization are starting to question Nitti's leadership. He decides to seek out someone who use to work for Al Capone, Walter Trager known as the Leaker, who has a knack for finding and closing down leaks in the organization.