Secrets come out and secrets stay hidden in Season 4, Episode 10. Don, Roger, Lane and Pete see their worlds start to crumble. And at least three of them engage in stunning displays of spinelessness. The one who shows some backbone is most surprising.

The 1960s references are everywhere in this episode. Don gives Sally a thrill when he tells her that he'll be taking her to the Beatles' concert in Shea Stadium (Aug. 15, 1965); Lane takes guests to the Playboy Club; the Cold War and the space race are key to a client's business; women sit in a doctor's waiting room to get an illegal procedure; someone makes the casual offer of a Valium; "Hazel" is playing on a television set. Yet it is the past that makes the biggest impact in this episode.

Big fat spoilers ahead about this packed episode.