Marshall offers to bet Barney "anything" that the secret is marriage. Barney will bet back that it's porn. He wants to bet $20,000. Marshall doesn't have it. After Lily rules out Marshall's potentially losing her virtue in a bet, Barney suggests a solution: the slap bet. Marshall is all excited, because he participated in slap bets when he was little. Lily doesn't understand. The (now-infamous) idea is that whoever wins gets to slap the other person in the face as hard as possible. Lily thinks it sounds "so immature," until Marshall offers her the post of slap-bet commissioner. This, she loves. Of course, the position entails involves resolving any disputes that may arise and imposing any punishments. Barney cautions her to put "the integrity of slap bet" above everything, because this is so important. "On your tombstone," he tells her, "it will read, 'Lily Aldrin: Caring Wife, Loving Friend, Slap-Bet Commissioner." Damn. That would be a great tombstone. Marshall says that Barney's will say he was slapped so hard by Marshall that he died. Death slap! Damn, Marshall.
Ted returns, asking whether he should just ask Robin if she's married. Lily tells him to drop it, and he agrees, which is how you know we're going to cut to him trying to pry it out of Robin -- which we do. He is using a complex Scrabble-based method of inquiry. Ted "casually" mentions to her that Marshall thinks she has a husband -- that Marshall is hilarious, huh? Huh? She wants to know if he's asking whether she's married. After some back-and-forth about privacy and secrets and the dangers of refusing to leave well enough alone, Robin announces that indeed, she is married. It was a mistake, but she is married. "Oh," Ted says miserably. Turns out he didn't want to know.
When we return, Ted is still shocked about the husband. Robin confirms that they were married at, and broke up at, a mall. And is she divorced? She says she's not -- the guy moved to Hong Kong for business, and she figured that was "good enough." Ted thinks this does not qualify as "good enough." Robin protests that it's not like she ever sees the guy. Unhappy but theoretically forced to be grateful for the truth, Ted promises not to tell anyone.