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.