As Ted recounts to his children the story of his meeting with their mother, his history with his four friends, Lily, Marshall, Barney, and Robin, unfolds.
Ted resorts to desperate measures to try and salvage his relationship with Robin, but his efforts prove distracting for Marshall. Barney is left to figure out how to get out of a relationship he didn't know he was in.
As Ted and Barney land in trouble with airport security, Lily has a confidence crisis when her outing with Robin showcases the latter's success with men.
As Ted looks to his old relationships in the hopes of finding his one true love, Barney and Robin have a bet that puts the latter's job on the line.
Marshall and Lily come up with their own plans as Robin invites the group to a new nightclub, but they soon come to discover that their friends' plans are better than theirs.
With their bar organizing their annual couples costumes competition, Robin has relationship problems with her boyfriend over her refusal to dress up with him. Ted and Barney continue searching for the former's elusive Halloween date from three years ago.
When Ted receives unexpected results when he tries a matchmaking service, he resorts to desperate measures to prove the results wrong.
Ted worries about his place in his own apartment as Lily moves in with him and Marshall and starts changing things. Barney tries to convince his friend to abide by a dating law that he came up with.
Lily has doubts about her place in Marshall's life during a visit to his family at Thanksgiving. Robin and Ted make a discovery about Barney's holiday plans.
After a wild night out, Ted has no recollection of what happened, forcing him to rely on his friends and the mysterious woman in his bed to piece together the events of the previous night.
When Ted gets a limo for a New Year's Eve celebration, the friends make their way from one party to another, but traffic only makes their plans difficult.
As Ted plans to bring Robin as his date to a wedding, his decision has unforeseen consequences as it nearly causes the wedding to be canceled.
After meeting a charming woman at the wedding, Ted pulls out all the stops to find her again as Robin confronts her feelings about that new development.
Ted and Victoria's new and exciting relationship causes Lily and Marshall to question their own. Robin acts as Barney's wingwoman for a night out.
A game night takes a turn as the friends try to figure out how Barney changed from the dedicated boyfriend he was to his first girlfriend to the playboy he is today.
Ted and Victoria's relationship runs into a hurdle when Victoria gets a job opportunity in Germany. Marshall and Lily confront the past as they discuss how they survived Lily's time in Paris.
As Ted tries to figure out how to navigate a long-distance relationship, Marshall's new job leads to a fight with Lily.
Filled with doubts about the fate of his relationship with Victoria, Ted joins Robin for a night out, much to Marshall and Lily's chargin.
When Robin invites her friends to an awards banquet, tensions rise as Ted has trouble dealing with seeing her with a co-worker, as Barney complicates Ted's life by hiring a call girl as his date.
When Lily and Marshall receive the news that their wedding may be earlier than anticipated, their search for the perfect band leads them to crash a high school prom.
Lily puts her wedding on the line as she acts behind Marshall's back. Ted has to figure out his feelings for Robin when the matchmaking service contacts him about a match.
Marshall confronts the danger that jeopardizes his and Lily's relationship. Ted decides to try and woo Robin.