On their way to Long Island for their wedding weekend, Robin and Barney come across a startling family discovery. Meanwhile, Marshall sees something online that changes the course of his journey east, while Lily confronts Ted about letting go of Robin.
When James reveals that he is getting divorced, Robin worries about how Barney will take the news. Meanwhile, Marshall races to find a way to get to New York in time for the wedding, and Ted deals with being alone at a romantic hotel.
When Lily discovers Ted's list of things he wants to do in New York before he moves for Chicago, she becomes frustrated that she is the only person who knows about his plans. Meanwhile, Robin and Barney realize they have very little time together before their relatives arrive for their wedding.
While Barney works through his anger at Ted after finding out he still has feelings for Robin, Marshall Skypes in to act as a judge and help settle their dispute. Meanwhile, Lily realizes she is Robin's only girlfriend.
Barney is upset after Robin wins James's wedding ring during the poker game, and Ted argues with Marshall and Lily over whether he gave them a wedding gift.
When Ted finds himself with three prospects to be his date for the wedding weekend, he chooses poorly. Meanwhile, Barney and Robin have a confrontation with their minister, and Marshall learns more about his driving companion, Daphne.
When Daphne sends a troubling text message to Lily, Marshall enlists the gang's help to remove the message while enforcing the "No Questions Asked" rule.
When Robin and Loretta's conflict escalates, Barney is caught in the middle. Meanwhile, Marshall and Daphne deal with a stowaway on their road trip, and Ted and Cassie try to enjoy a trip to a lighthouse.
During a flashback, the gang wonders how the Ted, Robin and Barney love triangle will play out; Barney accepts challenges from Robin and Lily.
Barney concocts a plan when his father arrives at the hotel; Ted thinks he is being framed when a wedding-related duty gets messed up.
Marshall tries to get Marvin to sleep by reciting rhyming bedtime stories.
Robin is dismayed when Barney wants to have their rehearsal dinner at a laser tag arena; Ted aggravates Lily by not following through with a promise.
A man at the wedding intentionally stirs up trouble; Marshall finally arrives at the Farhampton Inn.
In an attempt to deliver a devastating final slap to Barney, Marshall explains how he mastered the Slap of A Million Exploding Suns.
Robin and Ted try to get Barney to reveal secrets after he drinks too much; Marshall tries to avoid fighting with Lily.
The mother reveals how she met Ted and what she has been doing over the past eight years.
Robin and Ted reminisce about past relationships as they search for a drunken Barney on the day of the wedding; Lily and Marshall come to a resolution; Barney befriends two men who are eager to meet women.
The gang must figure out how to make the Stinson Hangover Fixer Elixir to help Barney recover on the day of the wedding.
Robin and Lily have a fight on the morning of the wedding; Barney can't decide what suit to wear; the gang watches a movie that Ted didn't want them to see.
Marshall asks Barney and Ted for help figuring out where Lily went in the middle of the night during their argument.
When Gary Blauman shows up at the wedding, it sends the gang into a frenzy as they each recall an encounter with him.
With only a half an hour left before the wedding, Robin and Barney panic; Lily and Marshall rewrite their wedding vows.
Ted finally finishes telling his kids the story of how he met their mother.
Ted finally finishes telling his kids the story of how he met their mother.