When the attempted assassination of small-time hood Smiley Barris, New York mobster Joe Kulak hires cold-blooded assassin Ray Quist to kill him. Ness tries to get Barris to cooperate but he refuses. When a second attempt on Barris goes wrong, Barris calls his Johnny Templar to help him out. Templar runs a gambling boat that goes out to sea beyond the three mile limit and beyond the long arm of the law. Templar hides his friend Barris on board so Joe Kulak turns the tables on both of them.

Frank Nitti and Bugs Moran are about to go to war, and to forestall that possibility, Elliot Ness and the Untouchables begin rounding up every machine gun owned by the gangsters' hitmen. To resupply himself, Nitti hires Polish gunsmith Jan Trobek to make a dozen Tommy guns. Unfortunately for Trobek and his wife, Nitti and Moran soon settle their differences, which means that the pair are now witnesses who could turn into liabilities for Nitti.