An old flame and potential client reenters Roger Sterling's life, Joan's husband searches for a new job, and Don finally comes clean to Betty about his true identity.

Don becomes frightened that his lie will be exposed when government agents question Betty about him, Lane has shocking news for his father when he comes to bring him home, and Joan considers having an abortion.

Betty discovers that she has a tumor, Peggy interviews an obnoxious young copywriter for a job, the firm tries to get the Mohawk Airlines account back, and Don and Harry try to court The Rolling Stones to record a commercial.

While Lane needs some help closing with a potential new client, Peter begins to crack under the pressure of both his home life and work life.

A depressed Betty tries to make things uncomfortable for Don and Megan, Roger tries to take out some secret weapons for a meeting with a prospective Jewish client, and Don makes a snap judgment that angers the creative department.

Lane searches for a way to get rid of a sizable debt, the firm prepares to pull out all the stops when it gets a second chance to land Jaguar as a client, and Don tries to comfort Joan when she reaches her breaking point.

As the partners consider expanding the office space, Don begins seeing ghosts and gets a request to advance Megan's acting career. Meanwhile, Peter's affair comes to a disappointing end, and Megan's mom briefly reunites with Roger.

As the firm prepares to go public, Don and Pete's actions cause them to lose two huge clients. However, Roger uses a new connection to put them in position to gain their biggest client ever.

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.

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.