Al Capone outwits Eliot Ness, but Capone's criminal empire remains in jeopardy when the IRS plants an undercover agent in his gang.

With Capone in jail, Frank Nitti, Paul Ricca and Joe Accardo take over. Meanwhile, a Hollywood scandal presents Sam Giancana with a chance to prove himself.

Joe Accardo sets his sights on Las Vegas, but the Outfit is threatened when Sam Giancona incurs the wrath of young attorney Robert F. Kennedy.

In the second-season finale, Joe Accardo and Sam Giancana have a falling out, and the fate of the Outfit rests on the outcome. Meanwhile, Joe Accardo cleans up loose ends before retiring.

In the second season opener, Johnny Torrio mentors Capone in Brooklyn, and then the two reunite in Chicago, where their bootlegging enrages local Irish gangsters.

A new mayor forces Torrio and Capone outside Chicago to nearby Cicero. There, Capone's brother Frank fixes an election, placing himself in jeopardy.

A betrayal destroys peace in Chicago and Torrio and Capone seek revenge against the Irish gangs. Meanwhile, the Beer Wars make Capone Chicago's top gangster.

Capone uses the St. Valentine's Day Massacre to assert his power over his enemies. Meanwhile, President Hoover takes notice; and dispatches Elliot Ness to take on Capone.