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.

When newspaper man Carlton Edmunds is gunned down on the street, the police and his friends initially think it's a case of being in the wrong place at the wrong time. Eliot Ness and his men soon determine that Edmunds was the target of a mob hit. His old friend, Floyd Gibbons, now a globe-trotting reporter, happens to be passing through Chicago and decides he's going to find the culprit. Working with Ness, they soon uncover that the hit was related to a series of articles Edmunds was planning on the takeover of the scrap metal business by the mob.