Changes at Sterling Cooper affect Pete and Ken. Don and Sal go on a business trip.
Betty gets a visit from her father. Sterling Cooper grapples with a very specific client request. Roger makes arrangements for a wedding. Peggy becomes personally affected by a campaign.
The writers fight off boredom when they are forced to work after hours. Roger hosts a party while Joan and Greg host a party of their own. Sally has a run in with Grandpa.
Gene and Don cross paths. Peggy is looking for a roommate. A wealthy new client has very high hopes.
Betty and Don deal with Sally. Pete pursues a new angle in business. Betty has a strange dream.
Sterling Cooper receives a surprise visit. Something is spooking Sally. Joan gets some unexpected news.
As Don secures an account with Conrad Hilton, Sterling and Cooper try to strong-arm Don into signing a contract. Meanwhile, Betty meets with her acquaintance from the governor's office, and Duck tries to get Peggy to leave Sterling Cooper.
Don and Betty renew their love affair while on a business trip to Rome, while Peter has a bout of infidelity with an au pair in his building while his wife is away.
Betty tries to meet with Henry Francis again, while Don steps up his pursuit of his daughter's former teacher. At the office, Don disappoints Conrad Hilton and is forced by a client to fire Salvatore over an unwelcome advance.
As Sterling Cooper prepares for its 40th anniversary party, the bosses in London drop a bombshell to Lane. Miss Farrell's troubled brother pays a visit to her and Don, and Betty stumbles onto her husband's secrets.
An old flame and potential client reenters Roger Sterling's life, Joan's husband searches a new job, and Don finally comes clean to Betty about his true.
Lane informs Pete that Ken has been appointed Senior Vice President in charge of Account Services. Although Pete makes his clients feel their needs are being met, "Mr. Cosgrove," Lane explains, "has the rare gift of making them feel as if they haven't any needs."
Don has an important meeting with Connie. Betty receives some advice. Pete talks to his clients.