This post contains mega-spoilers. Avoid—avoid!—if you haven’t seen this killer episode.

The next time someone puts together a special on Great Moments in Television, whoever it is had better reserve a choice spot for “Betty confronts Don.” The central scene of last night’s Mad Men cut to the heart of the show’s appeal on several levels: Don’s secret vulnerability, the shifting Betty-Don power dynamic, the notion that it’s impossible to escape your past. Normally, it would be the show’s m.o. to drop a bombshell and then ignore it for three or four episodes, which made the kitchen scene all the more shocking. For almost the first time in Betty’s presence, Don drops all artifice: He doesn’t make up any stories; he just crumbles. (Hamm’s performance is so textured, you almost wanted to hand him an Emmy on the spot.) Somehow Betty’s victory is tainted. Don’s explanation doesn’t invite forgiveness, exactly, but it paints him in a uniquely pathetic light. Even when she asks whether she should love him, his response is disarmingly frank: “I was surprised you ever loved me.”

In what context has Don eaten horse meat? Presumably in poverty growing up? It’s significant that he lets that fact slip in the meeting with Annabelle Mathis; maybe Betty is right when she suggests that Don did, on some level, want to be found out. The episode also beautifully counterweights Don’s past with the story of Roger’s fling with Annabelle. (Could the assonance of “Annabelle” and “Anna” be coincidental?) But unlike Don, Sterling manages to close off his past: He’s found something like happiness, and for the first time, we’re led to believe that he might truly be happy with Jane. One of the extraordinary things about the show is the way it turns empathy on and off like tap water. The only exception to that rule may be Joan’s husband, whose sole purpose in the show seems to be to repeatedly establish (a) that doctors can be assholes and (b) that otherwise smart women like Joan would put up with a lot of abuse for the premium placed on marrying one. (This week she caved and hit him with a vase, which felt like too little too late.)

Apart from that final cut—a genuine jaw-dropper (”And who are you supposed to be?”)—one reason the episode is so haunting is that it leaves such a profound sense of waste. In a single instant, Don’s marriage has changed forever. His blissful idyll with Suzanne is done, too, and she’s an innocent bystander; not only did she not turn out to be a ticking time bomb, but as Don says, she’s the only one who would think to ask how he’s holding up. And above all, the ghost of his half-brother Adam hovers over the proceedings. In light of Don’s confession to Betty, Adam’s death seems totally unnecessary. Could Don have brought him into their life, maybe changed his name too? The answer now seems like a qualified yes.

Early on, some complained that this season was too slow or uneventful, but that was crazy talk. The methodical set-up has paid off in a string of episodes that have registered like body blows. (It’s even more impressive when you consider that Peggy’s big revelation to Pete at the end of season two has gone virtually ignored; it’s kind of amazing that that doesn’t play like a big deal.) Where can Mad Men go from here? It’s hard to see how even a Kennedy assassination episode—which most presume will be the season’s finale—could top this.