With Prohibition coming to an end, gangster Milo Sullivan (Thomas Mitchell) gathers the hoods together and proposes a new money making venture. The mob will go into banking. They'll loan money to other hoods to stake high risk robbery ventures with the stipulation that they - "the bank" - get two dollars for every dollar they invest.
So fast forward a few months, and suddenly there are a rash of high dollar well prepared robberies happening, including one in which one million dollars in furs were stolen and a guard killed. Eliot Ness is brought in on the case. They start with a line up of most probable suspects and zero in on two who had large amounts of cash on them when arrested with no explanation. Before the bad new days of the cops being able to arrest the money and not the suspect so they could provide free daycare for said cops, Ness and company decide to follow these two suspects and see where it leads.
What ultimately does the underworld bank in is that it just can't help itself from being too greedy. They give the actual robbers a tiny amount of the take from said robberies, they kill somebody for not paying them back and then try to shake down the widow of the person they killed, and so on.
This was not the first thing Peter Falk was ever in, but it is about the only time I've ever seen him playing such a malevolent character. I also noticed Tony George as one of Ness' agents. He played minor roles in film and TV through the years, including a five year stint on daytime soap Search for Tomorrow.