Every time Marshall, Lily, Ted, Robin, and Barney hold a game night together, Marshall always wins no matter what the game is, so the others decide that he should always run game nights. Marshall decides to create his own game, "Marshgammon", which few people understand (although a player must drink if they ask "What?"). Ted plans to bring Victoria along, and tells Marshall, Lily, and Barney not to scare her off, despite the fact that, as pointed out by Barney, Ted hasn't told Victoria that he and Robin dated, nor of the story of the "re-return". All reluctantly promise not to ruin things, but Marshall uses the game questions to find out personal information about Victoria. Soon Lily mentions that someone gave her a videotape to give to Barney; when Barney finds out who, he panics, but "recovers" and calmly asks to have the tape. Lily gives it to him and he violently destroys it, but Lily reveals that she gave him a tape of Ted's graduation and hid the real one. Over Barney's objections, they watch the tape, and see a longhaired, hippie-ish Barney, playing a keyboard and singing a weepy, desperate love song to a girl named Shannon. Embarrassed and humiliated, Barney ejects the tape and walks out.
Barney meets all of them at the bar later, stating that that tape was the most embarrassing thing that happened to him. While the others want to know how it happened, Barney goads Marshall to confess an embarrassing moment. Marshall confesses that he was seen half-naked by Lily's kindergarten class after he unknowingly used a shared toilet in the school and was walked in on by another student from a different class. This leads Barney to tell the story that lead to the creation of the tape: in 1998, when he was 23, he was a hemp-wearing, peaceloving hippie who worked in a coffee shop with his girlfriend Shannon. "Saving themselves" for marriage, they had planned on going to Nicaragua with the Peace Corps, until Shannon failed to meet him on the night they were supposed to leave. He stops at this point, so to encourage him, Lily gets someone else to tell their most embarrassing story as well to take the pressure off of Barney. Marshall spins a game wheel he brought and it lands on Robin. She attempts to tell the story of the time she fell in horse poop on the news - but everyone else has already seen it. However, volunteering in her place, Victoria begins to tell a story involving a game of Truth or Dare, a squeeze bottle of marshmallow ice cream topping, and the hot tub at her grandparent's retirement community, but Future Ted does not recount it, stating that it is "too inappropriate".
Back to Barney's narrative: Shannon revealed to Barney that she backed out, saying that her father did not want her to go, because he has supported her and wants her to stay home. Barney left, but then went back to confront her dad, when she saw Shannon kissing an older man, which he presumed to be her father. To continue into the narrative, Lily tells the story of how Marshall's mother once overheard the couple having sex via a phone call. Barney then tells that he confronted Shannon and found out that she had begun seeing a yuppiealpha male named Greg, who got her out of her hippie "phase" and bought her stuff. She told him to go and forget about her. Barney postponed his departure instead and made the video and sent it to Shannon, but was humiliated when she and Greg returned and mocked him, and left the coffee shop devastated. Barney then changed his appearance and lifestyle, getting a haircut, wearing suits, and discarding his idealistic world-view. Finally, he goads Ted to tell his embarrassing story. Although Ted tries to speak of a summer trip to hide it, he relents and tells Victoria that he and Robin had dated at one point - and that on the night he told Robin he loved her he "re-returned" to her apartment to try and kiss her, but was so drunk that he threw up on her doormat and ran away instead. Although that does create some tension between Ted and Victoria, Barney deems it enough to finish his story: after he left Ted and Marshall's apartment with the tape, he visited Shannon, and found out that she has a son. He breaks down in tears, and Lily attempts to comfort him by assuring him that his own life isn't bad compared to Shannon's; Barney looks up, amused by Lily's words, and declares that his life "rocks" because he has money, suits, lots of one-night stands without a "brat" to take care of. He then brags that he finally had sex with Shannon, showing them all the video he took with his cell phone, and leaves, happy with the dirt he has acquired on all of them.
The episode closes with a montage which showcases happier moments coming out of the secrets between Marshall and Lily and Ted and Victoria. Next Barney is seen in the bar appearing jealous of a nearby couple, suggesting his words were really just a front to hide the fact that he might want a meaningful relationship someday, and finally Robin smiling at a new gift-wrapped Scherbatsky doormat. Over that shot, Future Ted hints that he would eventually come to learn of Robin's feelings for him, but that's another story.