24. "The Gypsy and the Hobo" (Season 3, Episode 11)
A pivotal episode for the ever-horrific marriage of Don and Betty Draper. She confronts him about his past, leading to a long night of grief, tenderness, and regret. Plus a very confused schoolteacher waiting outside in the car. (The teacher still ranks No. 2 on the list of Don's Exes Most Likely to Reappear at His Door with a Butcher Knife. Faye is No. 1.) When Don and Betty go trick-or-treating with the kids, their neighbor asks, "Who are you supposed to be?" Neither one has an answer.
Best line: "Look at you, figuring out things for yourself."—Joan Holloway Harris