On St-Patrick's Day, Ted follows Barney to a bar to party like there's no tomorrow, while Robin discovers something strange about Marshall and Lily's new apartment.
One of Barney's exes is sabotaging his love life, but he doesn't know who. So he makes a NCAA Basketball Tournament-style bracket to figure out which women he wronged the worst.
Marshall cries in front of his boss after he chews him out, and everybody gives Marshall their own unique advice on how to confront his boss about the situation.
Barney is upset because he violated his own "bro code" by sleeping with Robin. How will Ted react when he learns that Barney slept with his ex-girlfriend?
Barney finds a new wingman to replace Ted, but he's painfully shy and awkward around women. Meanwhile Ted discovers that his new girlfriend Stella hasn't had sex in 5 years.
Barney helps Abby get back at Ted by staging a fake proposal, but Abby doesn't realize that it's fake. Lily decides to sell some of her paintings so that she and Marshall can pay for floor repairs at their new place.
Ted breaks up with Stella but immediately wants to take it back after a life-changing experience. However, Stella doesn't realize that he broke up with her. Meanwhile, Barney has a serious accident on his way to see Ted in the hospital.
Ted and Stella get engaged, but Ted soon learns that he doesn't know anything about her. Meanwhile, Barney confesses to Lily that he's in love with Robin
Marshall claims that he had the best hamburger in the world during his first week in New York City, but he forgot where the burger joint is located. The gang then hits the streets of Manhattan to help him find it.
Ted does not want to move in with Stella because he hates New Jersey. Robin prematurely quits her TV job because she incorrectly thinks that she already has a new job.
Ted, Robin, Marshall, and Lily all begin getting cold feet because of their imminent life changes, and Barney tries to prove that he can pick up a woman while posing as an 80-year-old man.
Ted and Stella move up their wedding date, but the wedding may not go off as planned after Ted breaks the "No Exes Rule" and invites Robin to come in from Japan for the wedding.
Lily is disappointed to discover that Robin is secretly a "Woooo! Girl," and Barney secretly sabotages Ted's chance to get the contract to design a new bank skyscraper.
Ted tries to keep his irresponsible sister from hooking up with Barney during her trip to New York, and Robin starts hanging out with Marshall at a bar for Minnesotans, not telling them that she's really Canadian.