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.

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

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.

Luciano's decision to enter the prostitution business gives Thomas Dewey the chance to arrest him and put him on trial.

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 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.

Charles "Lucky" Luciano arrives in New York, teaming with Meyer Lansky and Bugsy Siegel. During Prohibition, Luciano's crew makes a fortune.

Luciano is found guilty of running a prostitution ring and goes to prison, leaving Vito Genovese as acting boss.

World War II begins, and the military asks Luciano to aid in the invasion of Sicily. Thomas Dewey considers letting him go.

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

"Lucky" Luciano gains power in the New York underworld during Prohibition. When two bosses start a mob war, Luciano plans to kill them both.

"Lucky" Luciano takes over the New York mob, organizing the Five Families. As Luciano's power grows, so does the attention from the Feds.

Luciano takes over Vito Genovese's heroin ring in Italy, then rejoins Meyer Lansky at a mob summit in Cuba. Genovese and Carlo Gambino plot against the mob leadership, and Bugsy Siegel's dream of Las Vegas turns deadly.

Vito Genovese and Carlo Gambino make their move. The police raid a mob summit, arresting Genovese. Gambino takes over.