In Brooklyn, New York, on 6 May 1918, young Alphonse “Al” Capone telephones the police to report a fur store robbery, but when two policemen arrive and grab the thieves, Capone breaks up the arrest and allows the robbers to escape. The policemen throw Capone through a window, cutting his face. They take him to headquarters and beat him until a corrupt judge telephones the commander with orders to let Capone go. Johnny Torrio, a Chicago, Illinois, gangster who is visiting Brooklyn mob boss Frankie Yale, suspects the young Capone set up the foiled arrest in order to get Yale’s attention. However, he respects Capone’s ambition and suggests that Yale “put him on the payroll.” When Torrio returns to Chicago, he tells his boss, Big Jim Colosimo, that the impending Prohibition laws will open a profitable new market beyond prostitution and gambling. Colosimo is not interested, because bootlegging alcohol would bring federal agents against him. Torrio telephones Yale in Brooklyn and asks him to send Capone to Chicago. When the young scar-faced gangster arrives, Torrio makes Capone his bodyguard and tells him to “take care of” Colosimo. After Capone kills Colosimo, Torrio takes over the operation, leases several breweries, and imports bootleg beer and whiskey into Chicago. Torrio tells Capone to stop acting like a thug, because from now on he will have to deal on a personal level with lawyers, judges, and politicians. In 1920, after gangsters murder two of Torrio’s liquor transporters, he meets with mob bosses Hymie Weiss, Dion O’Banion, and the Genna brothers to peacefully divide Chicago into territories and avoid future gang wars. At Torrio’s casino, Capone meets Iris Crawford, a free-spirited, inebriated “flapper.” Though she is rich and educated, Iris is drawn to Capone’s street-tough manner and bad reputation. Later, after the O’Banion gang kills a local gangster, the Chicago mob bosses, including Torrio and Capone, meet at the funeral to patch things up. However, Capone insults O’Banion, and O’Banion telephones several Irish assassins, including Bugs Moran, to “kill the Italians.” O’Banion’s gang raids the Genna brothers’ businesses and blows up one of their houses, with family members inside. Worried about his own safety, Capone hires a young bodyguard, Frank Nitti. One night, County Deputy Sheriff Joe Pryor shows up at Capone’s gambling house and demands $5,000. When Capone throws him out, Pryor and a dozen deputies raid the place and arrest both Capone and Iris. The next morning, Torrio’s lawyer, Jake Guzik, pays Pryor $5,000. Iris takes Capone golfing at her country club to clean up his image, and her wealthy girl friends are thrilled to meet a real gangster. Meanwhile, his men murder Dion O’Banion. In 1925, Nitti, hoping to gain his boss’s trust, plants dynamite in Capone’s car, then “finds” the explosives moments before Capone gets in. When Capone asks how he knew, Nitti said somebody knocked the rear-view mirror crooked. Johnny Torrio demands that all the killings stop before they attract too much attention from the authorities. However, Capone becomes angry during a mob meeting when Torrio splits his territory with Bugs Moran, Hymie Weiss, and Samuel Ettelson. Capone tells Nitti it is time to kill Torrio, but Nitti suggests that it would be better to give Weiss Torrio’s address and let him do the killing. Weiss only wounds Torrio, but the injuries are bad enough that Torrio turns his operation over to Capone. As Capone gains power, Chicago Crime Commissioner Frank Loesch comes to him to make sure the city’s gangsters do not interfere with upcoming elections. Capone continues to consolidate territory by shooting several men at one of Hymie Weiss’s clubs, but when a victim turns out to be a city prosecutor, the commissioner threatens Capone with a murder charge. Capone and Iris take a day trip into the country and make love in the woods. Afterward, she asks if he could take an abusive boyfriend of one her girl friends “for a ride.” When Capone agrees, Iris asks if she can watch. Later, Weiss’s gang retaliates, firing thousands of bullets into a restaurant where Capone and Nitti are eating. Capone responds later by hiring snipers to kill Weiss. Mobster Giuseppe Aiello allies his gang with Bugs Moran’s mob to retaliate against Capone, but an attempt to poison him at a restaurant goes awry. That night, as Aiello starts his automobile, it blows up. In 1929, Capone tells his men he is tired of seeing his friends murdered. He decides to wipe out the entire Moran gang in one operation. Using two men in police patrolmen uniforms, Capone’s mob raids Moran’s garage headquarters on St. Valentine’s Day, lines up nearly a dozen men against the wall, and shoots them down. The event becomes famous as the St. Valentine’s Day Massacre. Nitti tells Jake Guzik that Capone is out of control and needs to be reigned in before he wrecks the gang. Moran, meanwhile, tries to kill Capone, but his men murder Iris instead. Anton J. Cermak, soon to be the mayor of Chicago, calls Capone to his office, confesses he has already made a deal with Moran, and tells Capone to stop the violence. Soon afterward, Nitti takes Capone’s business ledgers to Cermak and tells him to turn them over to the Internal Revenue Service (IRS) and let “the Feds” take care of Capone. Sent to Alcatraz Prison in California, Capone is told by prison doctors in 1938 that he is suffering from “neuro-syphillis,” a disease that will destroy his mind before it kills him. Eight years later, in 1948, Frank Nitti visits his old boss in Palm Island, Florida. Capone, sitting by a swimming pool with a fishing rod, fails to recognize his old friend. He rails against the Bolsheviks. As Nitti leaves, he tells his own bodyguard, Tony, that Capone was stupid because he never watched the man in back of him, namely himself. Tony stands behind him, smiling, as he helps Nitti put on his coat.