In this series finale, Gyp Rosetti's alliance with Mafia don Joe Masseria backs Nucky into a corner and he is forced to cede control of one of his prized assets to Arnold Rothstein. Elsewhere, Lucky Luciano has to take on a new partner to help him smuggle and distribute heroin after being arrested in New York, while Chalky and Al Capone put their enmity on hold to take on Masseria's henchmen.