In May of 1966, Sterling Cooper Draper Pryce posts an equal-opportunity newspaper ad to mock Y&R over a racism scandal. The ad unexpectedly draws actual applicants, prompting SCDP to hire a black woman, Dawn, as Don’s new secretary. Roger tries to poach business from Pete, while Peggy argues with Don when he doesn’t support her in front of clients.
Megan throws Don a surprise 40th birthday party and stages a risqué song-and-dance performance. Don and Megan fight after the party but have passionate make-up sex the next day.
Joan visits SCDP with infant Kevin to ensure she hasn’t been replaced during maternity leave. Greg returns from Vietnam only to announce he’s going back. When Joan learns that he volunteered, she kicks him out.
Betty’s mother-in-law Pauline encourages Betty to lose weight. Betty visits the doctor for diet pills but the doctor discovers a thyroid lump which turns out to be benign.
Harry brings Don to a Rolling Stones concert to try and sign the band for a Heinz commercial, but mistakenly signs a lesser-known group.
Pete complains his office isn’t suitable for hosting clients and demands Roger’s, but Roger instead bribes Harry to trade offices with Pete. When Pete lands the Mohawk account, SCDP hires Michael Ginsberg as a copywriter.
Ginsberg pitches a Cinderella concept to Butler Footwear that Don had vetoed. The client loves the idea but Don scolds Ginsberg for pitching it without his approval. Feeling feverish, Don goes home early and dreams that he strangles a former lover. Peggy works late and discovers Dawn sleeping in Don’s office. She insists Dawn stay the night with her.
Lane fails to woo Edwin Baker from Jaguar Cars at a dinner meeting, so Roger, Don and Pete treat him to a brothel visit. The next day Lane reports that they lost Jaguar because Baker’s wife found out. Pete mocks Lane and they brawl.
Pete and Trudy host Don, Megan, Ken and Cynthia for dinner, where Ken admits his secret writing career. The kitchen faucet bursts due to a repair Pete had made, and Don fixes it. Pete flirts with a teenager in his driver’s ed class but is overlooked for a younger man.
Don excuses Megan from work to visit a Howard Johnson’s upstate. Once there, they fight over his insistence on controlling her life. Don angrily drives off without Megan and returns to find no trace of her except her sunglasses on the ground. Don searches for Megan through the night, but she’s taken a bus home.
Peggy delivers a pitch in Don’s absence and disappoints Heinz, who kicks her off the account. Flustered, she ditches work and has a sexual encounter with a stranger in a theater.
Roger and Jane take LSD and, while high, agree their marriage is over.
Megan shares an idea for the Heinz campaign with Don and stages an impromptu pitch with the client during a dinner, staving off their plans to fire SCDP. Peggy agrees to live with Abe.
Roger and Sally join Megan and her parents, Emile and Marie, at an American Cancer Society dinner where Don receives an award for his anti-smoking letter. Sally witnesses Marie performing fellatio on Roger in a back room. Emile urges Megan to stick with her dreams despite her success at SCDP. Soon after, Megan leaves SCDP to pursue an acting career.
At the train station, Pete meets Howard’s wife Beth and they have sex at her house. Pete tries to see her again, but she urges him to move on.
Betty attends Weight Watchers meetings and tells Sally about Anna Draper. Don reassures Sally that he and Anna were just friends, explaining that Betty is trying to hurt him and Megan.
Don and Ginsberg come up with Sno Ball taglines but Don only pitches his own. Roger convinces Jane to accompany him to a Manischewitz client dinner and they end up sleeping together, which she complains ruined her chance at a fresh start.
Lane learns that he owes £2,900 in back taxes and forges a $7,500 Christmas bonus check. Pete, meanwhile, announces that SCDP is back in contention for Jaguar.
Paul Kinsey invites Harry to a Hare Krishna gathering and begs Harry to pass his Star Trek script to a television contact, but Harry instead implores him to start a new life in L.A.
Joan explodes after she’s served with divorce papers. Don brings her to test-drive a Jaguar and they end up at a bar, where they reminisce.
Herb Rennet, who sits on Jaguar’s selection committee, tells Ken and Pete that SCDP will gain an advantage if he can spend a night with Joan. Pete broaches the proposal with Joan, and at Lane’s suggestion she consents, negotiating a 5% partnership stake in the company. SCDP wins the account.
Peggy accepts a job as Copy Chief at rival agency CGC. Don tries to dissuade her but fails.
Don tells Roger he wants bigger accounts and delivers a rousing pitch to Ed Baxter at Dow Chemical. Sally secretly spends time with Glen while Don and Megan are at work. When her period begins, she flees home to Betty.
Don discovers Lane’s forged check and demands his resignation, despite Lane’s protestation that he deserved the money. Lane attempts to commit suicide with exhaust from a new Jaguar that Rebecca bought him. When it fails to start, he hangs himself in his SCDP office, leaving a resignation letter.
The partners discuss expanding the office and Joan reports earnings are up. From Lane’s death-benefit payout to SCDP, Don re-pays Rebecca the $50,000 that Lane initially invested in the company. Rebecca blames SCDP for corrupting Lane.
Beth invites Pete to a hotel, where they have sex after she reveals she’s about to undergo electroshock therapy. The treatment erases her memory of him. Pete confronts Howard on the train and they fight. Trudy agrees to allow Pete an apartment in the city when he comes home battered from a supposed car crash.
Chaough puts Peggy on Phillip Morris’ “top secret” ladies’ cigarette and sends her to Virginia.
Don has a toothache and hallucinates visions of his dead brother Adam before having the tooth extracted.
Megan asks Don to help get her an audition for the Butler commercial. He says no but relents after watching her reel and Megan gets the job. He leaves Megan on the commercial set and goes to a bar, where a woman approaches and asks, “Are you alone?”