Lily meets an interesting person on the train to Farhampton, Marshall gets kicked off his flight to New York, Barney and Robin discover that they might be related, and Ted prepares to deliver a personal gift to Robin.
Marshall is forced to rent a car to get to New York, causing Lily to start drinking and accidentally reveal to Barney some bad news about his brother's marriage.
Barney and Robin try to have sex before the elderly wedding guests arrive, Ted reveals a list to Lily of things to do before he leaves New York, and Marshall has problems traveling through Packer Country.
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.
After Robin finds out her mother isn't coming to the wedding, the group recalls a fateful night six months ago when Barney accepted the "challenge" of a lifetime, and Ted made a decision about his pursuit of Robin.
Barney and James fight over which one of their fathers will get back together with their mom, Ted becomes a victim of "Zabkatage," and Daphne becomes inexplicably upset with Marshall.
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.
Robin and Ted take advantage of Barney when he becomes "truth serum drunk," and Marshall does everything he can to remain in "pause" with Lily and avoid their fight.
While out looking for 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.
Lily is concerned that Robin is not acting appropriately on her wedding day, Ted helps Barney pick his wedding suit, and the gang watch an embarrassing movie based on Ted's life.
The guys try to figure out where Lily went after her fight with Marshall and why. Meanwhile, after a talk with her mother, Robin is concerned that she is marrying her father.
With only half an hour to go, both Barney and Robin have panic attacks about their upcoming nuptials. Meanwhile, Marshall and Lily rewrite their old wedding vows.
After Barney and Robin's wedding, Ted builds up the courage to approach "the mother" at the train station. Meanwhile, three years after the wedding, Barney and Robin drop a bombshell on the group.
As the years go on, changes cause the group to drift apart, but they reunite one more time for Ted's wedding. Meanwhile, a monumental event causes Barney to finally change his ways.
