In the Season 3 finale, Nucky sacrifices a key asset to Rothstein in an effort to disrupt the Rosetti-Masseria alliance and take control of Atlantic City once again. Meanwhile, Luciano finds himself with a new drug partner after being arrested in New York; Chalky and Capone are unlikely allies in the war against Masseria; Harrow returns to Gillian's brothel to finish what he started; and Margaret tries to solve a romantic conundrum.