Based on the autobiography "The Untouchables," by Elliot Ness and Oscar Fraley, a young treasury agent assembles an incorruptible squad to dismantle the criminal empire of "Scarface" Al Capone.
Ness tries to get the influential president of a truckers union to stop mobster "Bugs" Moran and his crime syndicate from infiltrating the labor unions.
Eliot Ness is lured south of the border to retrieve a witness who will help his case. Only it's a set-up...once there, the mobster on trial is planning to have Ness killed.
A gangster who controls the produce market in New York has a colleague bumped off. But when the hit man he hired gets greedy, he has to get rid of him too.
After Dutch Schultz gets his income tax evasion trial moved to a quiet town, he starts to have a positive effect on its citizens and eventually sways the jury.
Eliot Ness and the Untouchables set their sights shutting down the numbers racket. The numbers are like a lottery where anyone can place a bet of up to one dollar on a three digit number. The payout for a full dollar bet is $600 so the profit for the mob, who run the racket, is the remaining 40%. Ness wants to shut down that cash flow which can be used for more heinous crimes. They think they may have an in when one of Al Morrissey's collectors is stabbed. Ness pressures Agent Marty Flaherty to make contact with Morrissey, an old friend who once saved his life. Before he can do anything, the Chicago police arrest Morrissey for gambling violations and Marty focuses on Al's son, Phil Morrissey but with little luck until his father pays the price for being connected to the mob.
Bank robber Frank Holloway escapes prison and travels across the country to rendezvous with his accomplice, but his various appointments with plastic surgeons prevent agent Eliot Ness from identifying him.
The mob seeks to relocate its base of operations outside of Chicago in a nearby community. Ness and his men move into the town intent on shutting the mob down before they get started.
An aging Mafia chief, Joe Bucco, is being pushed out of the organization in favor of his younger rival. But Bucco doesn't intend to retire without a fight.
An accountant with a brilliant mind for numbers agrees to testify against the mob. But keeping him safe before the trial keeps Ness and his men on the run.
The team faces a new kind of criminal when they battle the owner of the swank Jockey Club, a respectable gent who is the boss of the St. Louis underworld.
A newly released convict is blackmailed into running a slot-machine racket. If he refuses, his daughter will learn of his existence and be scandalized.
The department's newest agent is able to infiltrate the mob, using carrier pigeons to get information out. That is, until a woman gets him into trouble.
While a crazed derelict in Florida is obsessed with assassinating President Roosevelt, Capone's mob is planning to take over the Chicago World's Fair by killing the mayor.
Although unsuccessful in their first attempt to assassinate Chicago's Mayor, Anton J. Cermak, the Capone mob under the command of Frank Nitti and several other of the imprisoned mobster's lieutenants, have not given up. This time they hire a professional, Fred 'Caddy' Croner, an expert at using a long rifle with a scope who carries his weapon in a golf club bag. They put him on a retainer until Cermak goes out of town and sure enough, they learn that the Mayor will be traveling to Miami to attend a public event in honor of the President-elect, Franklin Delano Roosevelt, who is visiting the area before returning to Washington for his inauguration a few weeks later. Eliot Ness and the Untouchables are soon onto their plan and travel to Miami to protect Cermak. Unbeknown to them however, a crazed man, Giuseppe 'Joe' Zangara, has purchased a handgun with the intent to kill Roosevelt at the same public function.
The crime lords have now become money lenders. So when they cut one of their men out of his share of a heist, he comes after them...and so does Eliot Ness.