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.

An unlikely witness to the woods massacre threatens to expose the perpetrators, sending both Eli and Van Alden rushing to the hospital. Margaret starts a new job at an upscale French dress shop at the Ritz, while Chalky's team pays a heavy price for taking over Mickey Doyle's bootleg operation.

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.

Rothstein vents to Nucky and delivers a message to Gyp. Gaston Means sees an opportunity. Billie gets a new co-start. Van Alden and Sigrid receive an unexpected visitor. Gillian worries about her business.