Episode Six, "For Immediate Release"
For Don, the Holy Grail of advertising accounts has always been a car company like Chevrolet. When he finally gets the opportunity to pitch Chevy, the battle is lost before it's even been fought. Once Don and his nemesis, Ted Chaough, realize they're both going after the automobile giant, they know Sterling Cooper Draper Pryce and Cutler, Gleason and Chaough will cancel each other out. So over drinks in a Detroit bar, Don and Ted decide to pitch Chevy together, effectively merging both companies. The bombshell is dropped on Peggy in the final scene of the episode, when her former and current bosses announce she'll be moving back to her old work digs and she will once again be working under the mercurial Don Draper.