July 4, 1930. 40,000 horse racing fans fill Arlington Park. Eliot Ness and his men have Arnold "Spats" Vincent under surveillance. They will close in on him as soon as he gets a piece of paper with a list of names of officials in high places who are ready to do business with the crime cartel. Two hoods (one tall, one short), apparently associates of Spats, approach him. The tall hood sits next to him and whispers something to him, then he stabs Spats. The hoods take off running and Ness and his men and some cops chase them. They arrest the tall hood, but the short one gets shot by a cop.
Ness figures that top gangster Nate Stryker had put a contract on Spats. Ness and his men grill the tall hood, but he's not talking, he won't even give his name. Ness has Stryker hauled in but the tall hood won't squeal on him. Later, Stryker meets with Dexter Lloyd Bayless...he runs a school where he trains assassins. Bayless had provided the two hoods for this hit. Stryker is worried the hood might sing but Bayless just says he trains his killers too well for that.
July 12. The short hood, still unidentified, is buried as a "John Doe" in Potter's field. One night, a girl puts an anthurium lily on the grave. There are 294 florists in Chicago, so Ness and his men start checking them all. On the 3rd day, they find the florist who sold it. He describes the girl as 5'3", seventeen years old, with long, auburn hair and gray eyes. Unfortunately, that girl winds up as a "Jane Doe" in the morgue where she is finally identified as Linda Parish, who had a sometimes-boyfriend named Jimmy Chavis. Ness and his men visit Jimmy's parents, Julius & Catherine Chavis, to confront them that Jimmy was the short hood.
Ness, by checking with Jimmy Chavis' former employer, tracking down a retired bus driver who remembers where Jimmy got off, and finding a large painting of Bayless' mansion hanging on the wall in the Chavis home, finds Bayless' mansion, the school for assassins. Louis Mallet and Rick Tarro are two students who go there every day. As a cover for their stake-out, Ness gets Rico's sister to move into the house next door to Bayless.
Friday, August 22. Once again, in the secret basement training room, Bayless tells his students, "Come and kill me." They fight in the dark, using knives covered with protective cork tips dipped in chalk. But when the training session is over, the chalk marks show that Bayless "killed" them, while he is untouched. He shows them a chart of the human body and plunges a pointy-tipped cane into the heart.
Ness' visual surveillance and wiretap provide enough evidence for him to get an arrest warrant for Bayless. Ness leaves Capt. Jim Johnson and the police next door, and his team of agents outside and goes inside the Bayless mansion alone. In a reckless move, Ness follows Bayless down to the basement training room. Bayless hits the light switch, the room plunges into total darkness. Bayless taunts Ness, "Come and kill me." Bayless throws a knife at Ness, missing his head by inches. Bayless sneaks up behind Ness and starts choking him with a chain. Ness breaks free. They get into a knife fight but Bayless falls on his own knife. Ness had smashed the school for assassins.