It's January 1920. On the eve of Prohibition, Nucky Thompson, Atlantic City's Treasurer, condemns alcohol at a Women's Temperance League meeting. This is 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.

Straight-laced, uptight Agent Nelson Van Alden investigates a crime which he feels has been pinned on a scapegoat, so pays a visit to Nucky and leaves convinced that the Treasurer is "as corrupt as the day is long." Nucky quickly does damage control, enlisting his brother, Sheriff Elias Thompson, to close ranks with their underlings. Meanwhile, in Chicago, Al Capone shows a local reporter what he thinks about accusations that Johnny Torrio was involved in the hugging of local 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. Nucky evaluates his relationship with Lucy. Margaret starts a new job at a French boutique on the boardwalk. Meanwhile, Jimmy takes Nucky's advice to travel west.

Boardwalk Empire has more secrets about who's who. There is also a party afoot.

Eli, Margaret and Van Alden undermine Nucky's attempts to usher in a joyous St. Patrick's Day.

As Jimmy gets in with Johnny Torrio, Nucky takes a closer look at a theft on the boardwalk. Margaret stands up to Lucy.

Nucky has to revisit his childhood; Jimmy becomes allies with a veteran while the D'Alessio brothers get in good with Lucky Luciano.

Nucky travels to Chicago to attend the Republican National Convention, but events in Atlantic City distract his attention.

As Margaret continues to work for Madame Jeunet, Nucky realizes he has to battle a rival.

Van Alden becomes conflicted as his emotions get in the way of his work; Nucky requests that Margaret keep supporting his side. Also, Angela is shocked to see Jimmy's unhappy side.

Jimmy deals with some troubling family problems. Nucky shakes up the status quo. Van Alden deals with Agent Sebso's temptations.

Nucky wonders how much change Election day will bring to Atlantic City. Torrio tries to be the peacemaker between two bitter rivals with dire consequences. Jimmy, as well as Margaret, Van Alden, and Eli, ponder their futures.