On Valentine’s Day, 1962, Don's doctor warns him about living too hard, Betty meets Sara Beth's flirtatious friend Arthur, and Duck contends that Sterling Cooper needs younger creative talent. Don falters during lovemaking with Betty at a hotel. Trudy sobs to Pete about being unable to conceive. "Sex sells," responds Peggy a few days later after Don critiques her ad copy for Mohawk Airlines. He disagrees: "You feel something. That's what sells. Not sex."
Paul introduces Sheila, his black girlfriend, to his colleagues. Pete's father dies in an American Airlines jetliner crash that occurs the same day as John Glenn’s tickertape parade in Times Square. Duck convinces Roger to dump Mohawk Airlines and pursue American as a client. An anonymous coworker embarrasses Joan by posting her driver’s license on a bulletin board after she calls Paul's bohemian lifestyle phony.
When celebrity comic Jimmy Barrett insults the wife of their Utz client, Don's damage control includes sleeping with Bobbie, Jimmy's manager/wife. Harry discovers that Ken outearns him so he shows initiative by trying to hook up Belle Jolie with a controversial episode of The Defenders. Even though the deal falls through, Harry receives a raise and a promotion.
After Arthur expresses feelings for her, Betty cautions him not to jeopardize their friendship. Don tells Bobbie he'll ruin Jimmy if Jimmy doesn't apologize to Utz. Betty relishes playing the "shiny and bright" wife for Don.
Father Gill, Peggy's new parish priest, solicits her input on a sermon. Roger engages a hooker; Don and Bobbie have sex again. Duck's ploy to win the American Airlines account implodes when the airline fires his contact. Peggy's sister, Anita, tells Father Gill that Peggy had an illegitimate child; Father Gill hints to Peggy that he knows.
Pete and Trudy visit a fertility specialist; Joan gets engaged. Out celebrating Jimmy's TV deal, Don and Bobbie get into a car accident. Peggy bails Don out of jail; in a flashback, she recalls his help when she was institutionalized after giving birth. Bobbie advises Peggy to treat Don as an equal but reminds her to "be a woman." Trudy calls Pete immature when he belittles parenthood. Don's new secretary, Jane, is hired.
Playtex wants a sexier bra campaign, though its executives later reverse course. At Roger’s urging, Don and Duck call a truce over the American Airlines debacle. When Peggy complains about her exclusion from meetings and boys' nights out, Joan advises her to "stop dressing like a little girl." At a hotel, Don abruptly ties up, and then leaves Bobbie after she mentions other women have been discussing Don’s skills in bed.
The youth-culture insights of new creatives Smitty and Kurt help Sterling Cooper land an account with Martinson’s Coffee. Joan fires Jane for breaching office protocol and sneaking into Cooper’s office to view a Rothko painting. Afterwards, Roger reinstates her. Sal ignores his wife when the two have Ken over for dinner. At the Stork Club, Jimmy reveals to Betty that Don and Bobbie have had an affair and then confronts Don about it himself.
Don uses Betty as a marketing guinea pig with the Heineken account. After a troubled dinner party, she confronts him over his affair with Bobbie. Don feigns innocence. Joan reads TV scripts for Harry. Clients like her, but a new male hire gets the full-time position. Betty searches in vain for evidence of Don's affair. After seeing Jimmy Barrett on TV, she tells Don not to come home.
Don moves into a hotel. A drunk Freddy wets his pants, misses a presentation, then gets fired. Betty makes a lunch date with Arthur that she doesn't keep, leaving her friend Sara Beth alone with him. Don slugs Jimmy Barrett at an illegal gambling club. The next day Roger, inspired by Don's musings about moving forward with his life, leaves his wife for Jane.
Trudy, still struggling to conceive, wants Pete to consider adoption. He objects. Betty's father, who's had a stroke, accuses Don of disrespecting Betty. After sleeping with Don again that night, Betty still won't let him return home, so he accompanies Pete to California for an aerospace conference. Glen Bishop runs away from home, declaring that he's come to rescue Betty. The hardest part about divorce, Helen later tells Betty, "is realizing you're in charge."
Don abandons Pete at the conference for a Palm Springs affair with a young jetsetter name Joy. Roger plans his divorce and tells Duck his accomplishments to date don't warrant making him a partner. Kurt informs staffers he's homosexual and gives Peggy a haircut. Duck encourages two former colleagues from London to buy Sterling Cooper and anoint him president with control over creative.
Don visits the real Don Draper's wife; they reminisce in the house Don bought her years before, and he describes his current troubles. Pete rules out adoption and loses the Clearasil account after arguing with his father-in-law. Peggy brings in the Popsicle account, after which Roger awards her Freddy's old office. Sara Beth admits to "a terrible mistake" with Arthur. Joan's fiancé sexually assaults her in Don's office. Sterling Cooper's partners (minus Don) vote to merge with the Brits' firm.
As the Cuban missile crisis unfolds, a repentant Don reappears, but Betty, who has become pregnant, won't take him back, and has sex with another man at a bar. Duck overplays his hand at the merger meeting. Peggy tells Pete she gave away his baby. When Betty finally informs Don she's pregnant, he reaches for her hand and she takes it.