In the sitcom's second series, Ted (Josh Radnor) and Robin (Cobie Smulders) become a couple after finally getting together at the end of Series 1. Meanwhile, a heartbroken Marshall (Jason Segel) struggles to move on after his breakup with Lily (Alyson Hannigan), who ended their engagement in order to pursue an art fellowship in San Francisco. In other events, new information about Robin's past comes to light, and Barney (Neil Patrick Harris) engages in a "slap bet"—a wager in which the winner gets to slap the loser in the face as hard as possible—with Marshall.
The gang tries to help Marshall get over Lily, especially when he finds a credit card bill that leads to a hotel in New York City where some of her charges are listed.
Barney works with Marshall on his bachelor skills, which include hitting on women. Lily is back from her venture. Robin helps her look for a new apartment but gets sick of hearing about San Francisco.
Ted's parents visit New York for their anniversary and he learns a family secret. Robin worries that they won't like her. Lily and Marshall try to adjust to the new format of their relationship now that they are no longer together.
After Ted and Robin's first big fight, Barney tries to convince Ted that being an architect is an easy in to picking up chicks. Lily and Robin start following his trail after discovering that Ted hit it off with a girl named Anna shortly afterward.
Marshall tries to get used to being single in a world that is very coupled-oriented. Barney intended one-night-stand won't go away. Barney uses Lily to get out of his "horrifying" situation. Lily finds a place to stay.
Barney seduces Marshall's law professor in hopes of getting her to grade more leniently. Lily takes a job at Ted's office, where she promptly steals to teach Ted's boss a lesson.
Marshall goes on his first real date post-breakup with Lily. Not only do Ted and Barney try to warn him that this girl has got the crazy eyes, but Lily decides to do everything she can to find out about this her and break them up. Also, Barney gets a new name.
Marshall and Lily drag the gang to Atlantic City to elope, and their quest to overcome the three-day wait for a marriage license crosses them with some Chinese gamblers, a ship captain, and a sexy novelty shirt.
Ted and Barney discusses their viewpoints on knowing things about women. Barney thinks that the more you know the more likely you are to find a deal breaker. Ted wants to know the deal breakers right away, as Robin refuses to go to the mall to cover her secret.
Barney's brother, James (Wayne Brady), visits and Robin, the only one in the group that has never met him, is suprised. But James has a surprise for Barney that he finds difficult to swallow.
Ted almost ruins Christmas for everyone when, still carrying around anger toward Lily, he calls her a horribly disgusting name. Robin tends to Barney while he has a cold.
Robin wants to tell Ted that she loves him, but she can't tell him. Meanwhile, her sister visits and brings her boyfriend, and Robin doesn't know how to react when her sister says she's ready to lose her virginity.
When Ted is constantly insulted by his former boss, who is now working for him on a project, he is told to fire the man, but he finds that a hard thing to do. Meanwhile, Barney offers Lily a lot of money to paint a nude portrait of him.
When a funeral conflicts with the Super Bowl, the gang vows to avoid hearing the score and watch it together on Monday. This proves difficult, as Marshall is threatened with the score by a boy in Lily's class, while doing the news puts Robin in danger of finding out who won.
Ted can't seem to catch a flight to interview for his dream job and he and Robin contemplate why. The story unfolds backwards as they think about it they remember when Robin and Lily went hunting for a wedding dress and when Barney got stuck on the subway.
Lily gets asked to play in an off-off-off-off-broadway play, and the gang shows up to support her. Ted and Robin get hung up on what each kept from their past relationships. Barney performs his own play to prove a point to Lily.
Marshall is all set to celebrate his beloved Fiero hitting the 200,000 mile mark but it stops. While the gang sits in the mechanic's garage and waits to hear what will happen to the vehicle they think about times gone by that they have spent together in the car. We also get the story of how Ted met Marshall.
Barney takes drastic measures to prevent Ted from moving into Robin's apartment. Meanwhile, Marshall and Lily are discovering the ups and downs of having the apartment to themselves. Barney considers moving in with Marshall and Lily.
Robin attends Lily's bridal shower and finds the gift that she brought is out of place. Barney hires a stripper for Marshall's bachelor party.
Thinking that Bob Barker may be his father, Barney is overjoyed to be a contestant on The Price is Right. Marshall and Lily try sleeping apart prior to the wedding.
With everything going wrong on Lily and Marshall's wedding day, to everyone's surprise it's confirmed bachelor Barney who tries to fix it all.