Season synopsis
Contains spoilers for this season and earlier seasons.
Sterling Cooper is now controlled by British owners Putnam, Powell & Lowe, and Lane Pryce arrives to cut costs and reshape the office. Pete and Ken share the accounts leadership, turning their rivalry into a contest over who will keep the position. Don and Betty briefly try to rebuild their marriage around the birth of their son Gene, but Don begins an affair with teacher Suzanne Farrell. Sal is fired after he refuses client Lee Garner Jr.'s sexual demand, leaving Don to decide that Sterling Cooper can do without him.
Joan's marriage to Greg strains after he is passed over for a surgical promotion and enlists as an Army surgeon. Peggy grows more confident as a copywriter and increasingly expects Don to treat her as a colleague. After Betty discovers documents showing that Don was born Dick Whitman, she turns to Henry Francis and begins arranging a life apart from Don. Their relationship has already broken down, and the Kennedy assassination lands amid the family's preparations for Margaret Sterling's wedding, bringing private upheaval into a public shock.
Conrad Hilton tells Don that Sterling Cooper is being sold to McCann Erickson, which would end the independent agency Don has built his career around. Betty asks for a divorce, and Don decides he will not fight her. At work, he, Roger, Bert and Lane instead organize a new firm, using Lane’s authority to fire them and release them from their contracts, then recruiting colleagues. Peggy agrees after Don finally explains why he needs her, and Pete joins as well. The season closes with the group setting up Sterling Cooper Draper Pryce in temporary quarters.