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.
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.
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 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.
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.