Don and Megan take a trip to Hawaii for the holidays, Sally's friend visits the Francis family, a comedian torpedoes Peggy's Super Bowl ad campaign, and Roger gets some bad news about his mother.

Don strikes up a friendship with the surgeon in his building, Peggy tries to save her campaign, Roger makes a scene at his mother's funeral, and Betty goes to Manhattan to find Sally's friend.

While Don continues his affair with Sylvia, Pete's latest infidelity threatens his marriage. Meanwhile, Peggy's icy relationship with her new staff continues, but she also gets an unlikely tip on a potential new client.

Things quickly become awkward after the two firms merge, Don asserts his dominance over Sylvia, Pete has to deal with his ailing mother, and Bob Benson helps out a sick Joan.

The creative department has a wild, drug-influenced weekend as they work on the Chevy account, Don has trouble letting go of Sylvia, and Sally walks in on an unwelcome intruder.

Don is on the outside looking in on the forced indefinite paid leave from his job. While Ted heads back to New York for a few days, Don takes the opportunity to head to Los Angeles in part to meet with a California transformed Pete while he reunites with Megan, who is living full time there while pursuing what looks to be a promising acting career. Back in New York, Peggy avoids Ted at all cost while she learns to deal with the new "Don", Lou Avery, most specifically on the Accutron account for which she is getting consulting help from Freddie Rumsen. On top of that, she is also having to deal with being a landlady to who she believes are overly demanding tenants. Ken feeling overworked leads to Joan taking over his scheduled business meeting with Wayne Barnes, the new Head of Marketing for Butler Footwear. Barnes' news results in Joan taking what she hopes will be seen as decisive and preemptive action in overcoming a potential problem, action which she hopes demonstrates that she deserves to be more than just a glorified secretary. And Roger meets with Margaret on her request, the two who have been somewhat estranged over the last few months. Their individual new approaches to life may result in a friction-free reunion.

After a fight with Megan during a surprise trip to California, Don decides it's time to get back to work. Meanwhile, Betty joins Bobby on a field trip to a farm.

While Lou becomes the object of ridicule for the copy writers, Don tries to get away to California after a call from his pregnant niece. Meanwhile, the new office computer drives Ginsberg to the brink of insanity.

While Megan comes to New York with her mother and sister to collect her belongings, Don has a romance with the waitress. Meanwhile, Peggy and Stan work with a famous photographer on a commercial shoot.

Don decides to sell his apartment, Joan stumbles into a relationship while on a trip to Los Angeles, Glen tells Betty and Sally that he is going to Vietnam, and a copywriter gets in trouble for his rude behavior to a client.

Don goes AWOL from McCann Erickson in the middle of a meeting. Joan quickly gets fed up with the sexism at the new firm. Roger and Peggy put off reporting to their new jobs as long as possible.