Gyp makes his move in Atlantic City, forcing Nucky and Eddie to seek refuge with Chalky. With the Artemis Club overrun by Rosetti thugs, Gillian contemplates a business future that includes an unwelcome partner. Luciano makes a deal he’ll come to regret. Harrow loses his house privileges.

Nucky makes a deal with Rothstein as his war with Gyp Rosetti reaches its climax. Season finale.

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

Nucky plans to relocate to Manhattan; Margaret impresses Nucky and a grain company stockholder.

Nucky tries to hold onto his assets in Atlantic City; Willie and Eli become involved in Nucky's war.

Nucky tries to keep Jess Smith quiet and neutralize Gyp's alliance with Joe Masseria; Margaret considers an alternate future; Van Alden's side business backfires; Gyp's shipment is short; Chalky sees an opportunity.

Federal agents enlist the help of Eli and Van Alden to take down the Capone organization.

Nucky heads to Philadelphia; Agent Knox detains Eddie Kessler to obtain information about Nucky's organization; Gillian tries to score a fix; Van Alden is recruited by the Capones.

Nucky enlists Eli and Agent Knox to check the cargo in the Florida shipments; Margaret considers making a deal with Rothstein; Capone grows suspicious of Torrio; Nucky faces a dilemma.

Nucky faces Election Day in Atlantic City and pulls out all the stops to keep power in Republican hands. Torrio brokers a discussion between Nucky and Rothstein to resolve their growing gang war, as well as Rothstein's looming federal indictment over the World Series. Both Jimmy and Eli voice their growing resentment towards Nucky, and find they have an ally in the Commodore. Van Alden seeks a sign on whether or not to leave Atlantic City, but receives unexpected news from Lucy. Margaret weighs new information about Nucky's first marriage and her uncertain future to make a final decision on her role in his life.

January 1920. On the eve of Prohibition, Atlantic City's Treasurer, Nucky Thompson, condemns alcohol at a Women's Temperance League meeting, where he is noticed by Margaret Schroeder, a pretty, pregnant housewife who comes to him for help in getting her abusive husband Hans a job. Later that evening, the duplicitous Nucky privately tells his ward bosses about the opportunity to make huge profits selling bootleg liquor. At a countdown-to-midnight blast at Babette's Supper Club, he assures Jimmy Darmody, a recently returned WWI vet, that his appointment as "Man Friday" to the new Chief Clerk of the Fourth Ward, Paddy Ryan, will lead to bigger things. Jimmy, meanwhile, has higher aspirations and ends up making an alliance that could have dire consequences for both him and Nucky.

Esther Randolph's case is weakened by the sudden death of one witness and the sudden marriage of another. Jimmy turns away from the influence of others, including his mother. Nucky, acting the family man to Margaret, faces a difficult, bottom-line business decision.

After tracking down a liquor thief, Nucky and Owen spend a long night hiding out from the fedswith the precocious perp. In his boss’ absence, and with Rothstein fuming over a late delivery, Mickey overrules Eli to make a routing call that will have far-reaching consequences for Nucky and Gyp. Margaret encounters a familiar face while promoting Dr. Mason’s classes at the new women’s clinic at St. Theresa’s. In New York, Lucky haggles with Joe Masseria over heroin splits, while in Chicago, Capone’s feud with O’Banion heats up when one of his collectors gets roughed up on the South Side.

Gillian makes her peace with Jimmy's death; Van Alden attends a meeting with Capone and Torrio; Nucky makes an offer to Andrew Mellon; Margaret makes a stand on birth control; Nucky and Owen shop for a pony; Billie considers a future in film.

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.

After his father Ethan is injured in a fall, Nucky uses the opportunity to refurbish his childhood home. On a double-date with new friend Annabelle and her beaux, Margaret tries to get Nucky to open up about some painful childhood memories. During a visit to an army hospital, Jimmy befriends disfigured vet Richard Harrow, whose sharp eye proves invaluable. Van Alden gets a lead on the woods massacre.

Nucky is forced to readjust his political alliances with a Democratic mayoral candidate promising to wipe out corruption. Jimmy returns from Chicago to deal with the D'Alessio gang, which has allied with Rothstein to import European scotch through Atlantic City, but is arrested by Agent Van Alden for the massacre in the woods. Margaret intercedes with Nucky on Madame Jeunet's behalf, while Angela finds her romantic and artistic ambitions halted by Jimmy's return.

Nucky asks for Margaret's assistance in backing his mayoral candidate with the passage of women's right to vote, leaving her conflicted about her role. Doyle switches sides back from Rothstein, which leads Nucky to conspire with Chalky against Lansky and the D'Alessios. Angela witnesses Jimmy's violent side against her photographer friend, and considers leaving Atlantic City for good in the aftermath. Van Alden grapples with his emotions, and has encounters with both Margaret and Lucy.

Nucky vows to eliminate his nemesis. A high-profile bootlegger is arrested. Emily's birthday party is scaled down. Gillian blames Harrow for Tommy's trouble. Gyp decides to buy a town's silence.

Nucky refuses to back Chalky in a conflict; Gillian makes her custody case in court; Van Alden stands up to Capone and comes clean to O'Banion; Rothstein tries to make a trade.

Nucky and Margaret find common ground in Atlantic City; Luciano encounters an old adversary; Sally Wheet makes a payment in Cuba; in 1884, young Nucky moves up the Commodore's ladder.

Nucky makes a resolution; Margaret considers a hospital expansion; Gillian builds a new business; Van Alden stumbles onto a confrontation.

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 train-station 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, vowing to exploit Nucky's weakest link. Chalky is intrigued by Daughter Maitland’s presence. Dunn Purnsley goes to Harlem, and is courted by Valentin Narcisse. Willie and his college roommate, Clayton, carry a practical joke too far.

On the day of the annual St. Patrick's Eve dinner, Nucky deals with Eli's oratory ambitions, as well as a group of disenchanted "Leprechauns". Feeling ignored by Nucky, a frustrated Margaret feeds Van Alden information. In Chicago, Jimmy copes with the aftermath of a vicious attack orchestrated by Torrio rival Charlie Sheridan.

Despite being publicly embarrassed by legal trouble, Nucky's biggest concern may be holding on to his private army in a battle for control of Atlantic City. Meanwhile, Jimmy pitches a business deal to Arnold Rothstein in New York, but may have more in common with Meyer Lansky and Lucky Luciano. Margaret draws on past experience to retrieve some valuable information, Chalky clashes with a fellow inmate, and an Irish nationalist comes to town looking for support.