January 1920. On the eve of Prohibition, Nucky Thompson, Atlantic City's Treasurer, condemns alcohol at a Women's Temperance League meeting. Later that night, the duplicitous Nucky tells his ward bosses about the opportunity to make huge profits selling bootleg liquor.

Agent Van Alden investigates a crime he feels has been pinned on a scapegoat, convinced the Treasurer is as corrupt as the day is long. In Chicago, Al Capone shows a reporter what he thinks about Johnny Torrio being involved in the killing of mobster "Big Jim" Colosimo.

As a witness threatens to expose the partakers in the woods massacre, Nucky, Van Alden, and Rothstein take special interest in a hospital patient who may know something about the massacre. Chalky's take over of Mickey Doyle's bootleg business gets off to a rough start.

In Chicago, Jimmy bonds with one of Johnny Torrio's prostitutes and finds himself increasingly at odds with the hot-headed Al Capone. Back in Atlantic City, Nucky looks to leverage his relationship with U.S. Senator Walter Edge, as well as Jersey City Mayor Frank Hague.

Nucky deals with his jealous brother's oratory ambitions. Feeling ignored, a frustrated Margaret feeds Van Alden information. Arnold Rothstein worries about his involvement in the fixed World Series. Jimmy copes with a vicious attack orchestrated by Charlie Sheridan.

Nucky turns up the heat on Lucky Luciano after one of his ward bosses is robbed. In Chicago, Al Capone's frustration over family issues spills over into his relationship with Jimmy, who scores points with Johnny Torrio for a bold power play involving Charlie Sheridan.

After his father in injured, Nucky uses the opportunity to refurbish his childhood home. Jimmy befriends disfigured vet Richard Harrow, whose sharp eye may prove invaluable. Van Alden gets a lead on the woods massacre. Luciano and a buddy cut a deal with the D'Alessios.

While visiting Chicago during the Republican National Convention, Nucky gets some alarming news from Atlantic City.

Nucky braces for war with a rival faction; Jimmy stands by his alibi; Margaret helps out Madame Jeunet.

Nucky asks Margaret to toe the party line; Angela witnesses Jimmy's violent side; Capone faces a crossroads; Van Alden grapples with his emotions.

Nucky shakes up the status quo; Jimmy deals with some tricky family issues; Van Alden addresses Agent Sebso's "temptations".

Nucky and Atlantic City brace for change on Election Day. Torrio brokers a deal between two nemeses, with far-reaching consequences. Jimmy ponders his future, as do Margaret, Agent Van Alden and Eli.