1929. Notorious gangster boss Charlie Radick is dying of leukemia. There will be no mourning for him while the other overlords will be vying for his throne. All Radick wants to do is see his long-lost daughter before he dies. Eliot Ness visits Radick because he's afraid a gang war might break out as the rival gangs scramble to take over. Ness says, "Turn over your books to me; names of the people in your organization, distribution points, contacts in City Hall." Radick says while he was in prison, he left his daughter with a couple but three years ago she ran away. Radick tells Ness, "Find Margaret, and I'll give you everything you ask for." Ness never makes deals with hoods but this time the gangster isn't asking for a break, or to plea bargain, he only wants Ness to find his daughter. Ness doesn't promise him anything, but he starts the search.
Ness is getting help from Lt. Agatha Stewart and Frank...they do some legwork, and find out Margaret Radick is now going by the name Margaret Wilson. The trail leads to the slums of Chicago where Lt. Stewart checks out an apartment complex where Margaret lived, there is a "building condemned" sign hanging on it. Lt. Stewart talks to a little girl named Amy. When the building manager comes out, Amy says to Lt. Stewart, "He's my father...he drinks beer." The manager says Margaret had a kid out of wedlock. Then Amy sneaks over to the Green Cat nightclub, where Margaret is. Margaret is a gorgeous lady, about 30, and she's having drinks with a customer. That night, at the pier, Charlie Radick is being set up for a rubout by his own man Millerick, who is one of Nitti's lieutenants, Vadney, is about to shoot him, when Ness fires first. Radick asks Ness what he's doing. Ness tells him he's providing protection. Ness wants to keep him alive, so he can get the mob records.
Back at the Green Cat club, Lt. Stewart is talking to Amy. She finds out that Margaret's baby was taken away from her, probably by the child welfare people. Furthermore, Margaret just left for the bus depot. She wants to go to Denver. Lt. Stewart finds her there and they talk. Margaret says that when her father went to prison, he told her "you're all I've got," and promised that "someday I'll come back for you." That was her dream, her hope. But her father deserted her. Ted Clemens is the father of her child, but he refused to marry her. Ironic, that while Clemens failed in his duty as a father, it is Margaret who was declared an unfit parent and had her child taken away from her. "I took care of my baby," says Margaret, "and when they took her away, I just didn't care anymore." Margaret resented her father for deserting her...now, Margaret had deserted her child. She had become like her father.
Ness is at the hospital where Radick is dying when Margaret shows up. Radick says, "I owe ya, Ness," and gives him the key to a safety deposit box which has his book, detailing everything about the mob and its operations. For many years, Margaret just wanted to be with her father. Now, she is meeting him out of spite, to show him what she's become. Radick says he just wants to take a look at her. Margaret snaps spitefully, "Take a good look." But then she realizes that, just as her father had once said she is all he's got, her father is all she has, too. She forgives him, and they embrace. Eliot Ness, his job finished here, goes off to get the records and shut down the mob.