Bugs Moran, hiding out since Al Capone eliminated his gang in the St. Valentine's Day Massacre, is visited by Eddie O'Gara, a man he thought had been killed by rival gangsters several years previously. Although he never cared for O'Gara in the first place, Moran is intrigued when Eddie lays out a plan to put Moran back in charge of the rackets again. Meanwhile, Elliot Ness is looking for Moran and O'Gara, figuring that both will want revenge on the gangsters who are responsible for their plight and that he can use that to destroy the Chicago syndicates permanently.

After a mobster with valuable information is killed in broad daylight at the racetrack, Eliot Ness and his men try to identify the killer. No one will admit knowing him but by tracing his movements, they find he was a regular visitor to the home of Dexter Lloyd Bayless who lives in a well-to-do suburb of Chicago. Through surveillance, they note that he has regular visitors in the afternoon and Ness decides to break into the house to plant a listening device. Through that, they learn that Bayless is running a very special school out of his home: a school for assassins.