(Season Four Premiere) Having survived his epic battle with Gyp Rosetti, Nucky makes a peace offering to Joe Masseria while working the odds with Arnold Rothstein. Chalky prepares to open the Onyx Club on the Boardwalk;a fresh-faced prohibition agent, Warren Knox, arrives in Atlantic City to learn the ropes; Richard Harrow returns to his violent ways.
Now working as a delivery man for Dean O'Banion, Van Alden is ordered to keep tabs on Al Capone. Harlem gangster Dr. Valentin Narcisse arrives in Atlantic City, clashing with Chalky and Nucky. In Washington, Agent Knox aligns himself with J. Edgar Hoover. Harrow fails to finish a job in Milwaukee, while Eddie demands a promotion.
Nucky has reservations about investing in a Tampa land deal. While there, he befriends local speakeasy owner, Sally Wheet. Valentin Narcisse books a sexy jazz singer, Daughter Maitland, to perform at the Onyx. Willie, Eli's son, turns to Mickey Doyle and his bootleg warehouse to elevate his social standing in college. Harrow tries to bury his past.
Nucky gets to know Arnold Rothstein over a card game, and sizes up an unexpected partner for his Tampa land deal. A newly promoted Eddie Kessler gets detoured after making a delivery. When one of their collectors is incapacitated, Al and Frank Capone decide to finish his route, enlisting a reluctant Van Alden to tag along. Agent Knox fills Hoover in on the Thompson operation.
Nucky heads to Philadelphia to deal with the fallout from Willie's liquor fiasco. Eddie Kessler is detained by Agent Knox, who uses physical and psychological tactics to elicit information about Nucky's organization. A desperate Gillian turns to an unexpected source to score a fix. In Cicero, Van Alden is recruited by the Capones for a job.
After a cautious reunion with Margaret, Nucky heads to Tampa to work out details of his land deal with Bill McCoy. While there, he reconnects with Sally Wheet. Richard Harrow returns to Atlantic City. Having lost J. Edgar Hoover's confidence, Agent Knox finds a new way to gain Eli's trust. Meyer Lansky decides to go it alone on the Tampa land deal.
Eli confronts Nucky after Willie makes an unpopular decision. Margaret has a surprise encounter at her job. Joe Masseria orders Lucky Luciano to deal with Vincenzo Petrucelli. Gillian goes cold turkey. Al Capone tries to get Johnny Torrio to turn on rival gangster Dean O'Banion. Valentin Narcisse exerts his control over Dunn Purnsley and the Northside.
Nucky's shipment from Florida arrives with some unexpected cargo. Eli is backed into a corner after Agent Knox uncovers some new dirt on the Thompsons. After talking things over with Nucky, Willie reconsiders his recent life choices. Chalky throws down the gauntlet toward Valentin Narcisse, upholding his leadership on the Northside.
Nucky refuses to back Chalky in his conflict with Narcisse. Julia considers her options after Gillian makes her custody case in court. In Cicero, Van Alden stands up to Capone and comes clean to O'Banion. Rothstein looks to trade an insurance benefit for a cash infusion.
Tipped off by Sally Wheet, Nucky enlists Eli and Agent Knox to check out extra cargo in Florida shipments. Margaret considers making a deal with Rothstein to improve her family's living conditions. Capone grows suspicious of Torrio; Nucky faces a dilemma; Eli makes peace with Willie.
Nucky takes inventory after being warned there's a skunk in his cellar. On the lam after a close call, Chalky and Daughter take refuge outside Wilmington with Chalky's mentor from years ago, Oscar Boneau. Gillian weighs selling her mansion and starting a new life with Roy Phillips.
Season Four Finale. Eli braces for the worst as Agent Knox sets in motion his plan to take down Nucky. Capone and Torrio reach an agreement in Cicero. Chalky looks to settle his scores. Richard Harrow steps forward to save Tommy, at Gillian's expense.