Don accidentally learns a secret about Salvatore during a business trip to Baltimore. Back at the office, the firings continue, but the new management appoints Peter and Ken as new co-heads of accounts.
Don is brought in to save the day for a P.R. campaign involving the building of the new Madison Square Garden, only to have the rug pulled out from under him. At home, Betty argues with her brother over how to care for their sick father.
Roger Sterling throws an expensive party with his new wife, Joan throws a dinner party, Peggy and Paul get stoned while working on an ad campaign, and Don's daughter Sally steals money from her grandpa.
Don has reservations about a misguided potential client who wants to sell jai alai as the "new national pastime." Meanwhile, Sal produces the "Patio" television commercial, Peggy searches for a roommate, and Betty's father passes away.
Betty has hallucinations of her dead father as she delivers her baby, Peter considers trying to sell the untapped "Negro market" to a reluctant client, and Peggy begins to question her future at Sterling Cooper.
The bosses come in from London to reorganize Sterling Cooper, but a key player's career is sidetracked by a freak accident. Meanwhile, as Joan prepares to leave her job, her husband gives her some bad 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.
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.
On the weekend of the John F. Kennedy assassination, Pete finds out that he lost the promotion to Cosgrove, Roger Sterling's daughter's wedding goes off as planned, and Betty musters up the courage to respond to Don's confessions.
With another sale on the horizon, Sterling, Cooper, and Draper convince Lane Pryce to fire them and then join them as they start up a new advertising firm. At home, Betty follows through with her plans to divorce Don.