Following his battle with Gyp Rosetti, Nucky makes a peace offering to Joe Masseria while working the odds with Arnold Rothstein. While Chalky is busy running the Onyx Club on the Boardwalk, the impulsive Dunn Purnsley clashes with a booking agent. Fresh-faced Federal Agent Warren Knox arrives in Atlantic City to learn the ropes from Agent Sawicki. Gillian seeks custody of her grandson, Tommy, while trying to find a “good” man to keep the Artemis Club afloat. Eli’s college-age son, Willie, turns to Nucky for career advice. Al Capone enlists his brothers, Frank and Ralph, to help him expand his business in the Chicago suburb of Cicero. 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, joining the ascendant mobster to help keep Cicero voters “informed” at a political rally. Dr. Valentin Narcisse arrives in Atlantic City, clashing with Chalky and Nucky over the loss of an employee. In Washington, Agent Knox aligns himself with J. Edgar Hoover, acting director of the Bureau of Investigation. Harrow fails to finish a job in Milwaukee, while Eddie demands a promotion after 11 years of service. With a business opportunity on the horizon, Nucky departs for Florida.
Nucky has reservations about investing in a Tampa land deal engineered by transplanted bootlegger Bill McCoy. While there, he meets speakeasy owner Sally Wheet. Valentin Narcisse books a sexy jazz singer, Daughter Maitland, to perform at the Onyx, and gauges Dunn Purnsley’s allegiance to Chalky. Willie, Eli’s son, turns to Mickey Doyle and his bootleg warehouse to elevate his social standing at college. Gillian agrees to pose as Roy Phillips’ wife to impress a possible partner. Harrow tries to bury his past, though not before taking care of some unfinished business with Emma.
Nucky goes to Philadelphia to deal with the aftermath of Willie's ill-fated prank; Eddie endures a marathon detention by Agent Knox; Gillian's desperation for a fix takes her to an unfamiliar part of town; Van Alden works for Al Capone on Election Day at a factory outside Chicago.
After a cautious reunion with Margaret in New York City, Nucky heads to Tampa to work out details of his land deal with Bill McCoy and reconnects with Sally Wheet. Richard Harrow returns to Atlantic City and makes a confession to an ailing Paul Sagorsky, who encourages him to get over the past and return to Julia and Tommy. 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 when Lucky Luciano gets spooked by Vincenzo Petrucelli, an investor with ties to Joe Masseria in New York. Chalky takes out his frustrations on Daughter Maitland.
Eli confronts Nucky after Willie makes an unpopular decision. Margaret has a surprise encounter at her job on Wall Street. Joe Masseria orders Lucky Luciano to return to Tampa and deal with Vincenzo Petrucelli. Gillian goes cold turkey with Roy Phillips' help. Still seething over his brother's death, Al Capone tries to get Johnny Torrio to turn on rival gangster Dean O'Banion. As the relationship between Chalky and Daughter Maitland deepens, Valentin Narcisse exerts his control over Dunn Purnsley and the Northside.
Nucky's shipment from Florida comes with some unexpected cargo; Eli feels the heat from the Feds when Knox uncovers new evidence of the Thompsons' escapades; Willie reconsiders his recent choices after a talk with his uncle; Chalky clashes with Narcisse over control of the Northside.
Tipped off by Sally Wheet, Nucky enlists Eli and Agent Knox to check out the extra cargo in Florida shipments. Margaret ponders 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 of a skunk in his cellar. On the lam following a close call, Chalky and Daughter take refuge outside Wilmington with Oscar Boneau, his mentor from years ago. Gillian considers selling her mansion and starting a new life with Roy Phillips.
Eli braces for the worst as Agent Knox launches his plan to bring Nucky down. Capone and Torrio reach an agreement in Cicero. Chalky looks to settle scores. Richard steps forward to save Tommy, at Gillian's expense.