Travelling to Long Island Robin and Barney come across a startling family discovery and Lily doubts Ted really has let go of Robin.
Robin worries about how Barney will take the news that his brother is getting a divorce. Meanwhile Marshall tries everything he can to get to the wedding in time.
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 has to pick a side when Robin and his mother have a fight. Lily has a word with Barney about not ruining his relationship to help him make a decision. Ted and Marshall get in a far less serious argument over wedding gifts and thank-you notes.
Ted chooses poorly out of the three prospective dates he has for the wedding weekend. Barney and Robin fall out with their minister. Marshall finds more out about Daphne.
Lily receives a troubling text off of Daphne leading to Marshall getting the help of the rest of the gang to try and delete the message, whilst trying to enforce the 'No Questions Asked' ruling.
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
In a flashback episode, the gang ponders the future of the Ted, Robin and Barney love triangle. Meanwhile, Barney accepts a series of challenges from Lily and Robin
When Barney's father arrives at the hotel, Barney devises a plan that makes Robin very nervous. Meanwhile, Ted is convinced someone framed him by messing up a wedding-related duty
Marshall tries to get Marvin to sleep by reciting three rhyming bedtime tales about his friends as they wind down their epic cross-country journey.
Barney becomes fixated on having his rehearsal dinner at a laser tag arena, much to Robin's dismay. Meanwhile, Ted doesn't come through on a promise, which aggravates Lily
The gang encounters a guy at the wedding who intentionally stirs up trouble among them, and 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
When Barney drinks too much, Ted and Robin take advantage of him and get him to reveal secrets he's been hiding for years. Meanwhile, Marshall does everything he can to avoid fighting with Lily
On the 200th episode, The Mother recounts how she met Ted and what she's been up to for the past eight years
While out looking for an inebriated Barney on the day of the wedding, Robin and Ted reminisce about past relationships. Meanwhile, Marshall and Lily finally resolve their issues and Barney befriends two young guys eager to meet women
Barney suffers from the world's worst hangover on the morning of his wedding. The gang tries to figure out and find the bizarre ingredients to concoct the Stinson Hangover Fixer Elixir.
On the morning of the wedding, Lily and Robin have a fight and Barney freaks out about which suit to wear. Meanwhile, the gang watches a movie Ted has forbidden them to see
Marshall enlists Ted and Barney to help him figure out where Lily went when she left in the middle of their fight
When Gary Blauman shows up at the wedding, it sends the gang into a frenzy as they each recall an encounter with him