By 1927, Al Capone has risen from a no-name accountant to the head of the Chicago mafia in less than a decade. His criminal syndicate now rakes in over 100 million dollars a year.
Despite his success, Capone is still running his operation out of the neighboring suburb of Cicero. He knows that if he's going to consolidate power as king of the underworld, he needs to move back to where it all started: Chicago.
Nearly four years earlier, Capone was driven from Chicago by Mayor William Dever, a man who'd sworn to clean up the city. But with a wave of recent gangland violence, Dever's popularity is plummeting. Capone takes his revenge by heavily funding Dever's opponent, corrupt former mayor Big Bill Thompson, in the mayoral election.
Capone's strategy pays off and Thompson wins easily. Capone moves back to Chicago and takes over two floors of the city's finest hotel, the Lexington. With a thriving business and Chicago politicians in his back pocket, Capone soon reaches a level of celebrity normally reserved for athletes and entertainers. As Capone's profile grows, he begins to indulge in all that the Roaring '20s have to offer, including cocaine.
While Capone enjoys his reign at the top of the Chicago underworld, Irish gangster Bugs Moran seeks to take him down as revenge for the deaths of his partners Dean O'Banion and Hymie Weiss. On March 7, 1928, Moran orders a hit on one of Capone's top associates, Jack McGurn, the man who took out Hymie Weiss. McGurn survives but Capone decides to retaliate by taking out Moran and as many of his men as possible - all at once.
Capone's crew comes up with a simple solution, but one that requires meticulous planning. They enlist Chicago's top two Sicilian hit men, John Scalise and Albert Anselmi, to carry out the operation. They arrange for one of their trusted liquor dealers to set up a buy with Moran. With all the pieces in place, Capone conspicuously leaves for Miami to distance himself from the hit.
On February 14, 1929, Capone's men dress as law enforcement and raid the liquor buy. They order Moran's men to face the wall for handcuffing, but while their backs are turned, Capone's men shoot all of them. Firing 70 rounds of ammunition in less than 10 seconds, the assassins carry out the biggest gangland hit in American history that will come to be known as the St. Valentine's Day Massacre. Through a stroke of luck, Moran avoids the massacre, but knows he's been defeated.
After five years, Capone has finally defeated the Irish. But the victory comes at a cost: the massacre's press brings unwanted scrutiny -- not just to Capone's organization, but to the entire mafia.
The mafia advises Capone to lay low, but Capone ignores the warnings. Fueled by a growing drug habit, Capone continues to do as he pleases and soon even his most trusted associates begin to question his authority. Anselmi and Scalise begin forming alliances with other gangsters to get rid of him. When Capone learns of their betrayal, he beats them to death in front of his associates, warning his men of the consequences of disloyalty.
As news of the brutal killing spreads within the underworld, mafia leaders from back east become fed up with Capone's antics. New York crime boss Lucky Luciano organizes a top secret meeting in Atlantic City, inviting mob bosses from across the country to decide how to deal with Capone. While most mobsters favor eliminating Capone, Luciano sees another way: send Capone to jail.
With the rest of the mafia turning against him, Capone knows he has no choice but to take the fall. For his own protection, he gets himself arrested and spends 10 months at Moyamensing Prison in Philadelphia.
Following the public outrage from the St. Valentine's Day massacre and the recent onset of the Great Depression, President Herbert Hoover declares war on Capone and goes after Capone for Prohibition violations. Leading this operation is Eliot Ness, an ambitious young agent just three years out of college, who's already distinguished himself as an undercover operative. As Ness takes charge of the operation, he uses surveillance, anonymous tips and wiretaps to build his understanding of Capone's operations.
On June 13, 1930, Ness raids one of Capone's breweries. Capone tries to buy off Ness, but Ness refuses. After turning down Capone's bribe, Ness and his team come to be known as the Untouchables. Over the coming months, Ness's team of agents raids Capone's breweries and also targets his trucks, destroying and seizing upwards of 200,000 gallons worth of beer.
Feeling the pressure from Ness's raids, Capone orders a hit on Ness. As Ness drives down an empty road, Capone's men close in on Ness with two cars and force him off the road. Ness crashes into a tree.