The popular sitcom's ninth and final season transpires almost entirely during the wedding weekend of Barney (Neil Patrick Harris) and Robin (Cobie Smulders). The series moves to Long Island as the happy couple and married friends Marshall (Jason Segel) and Lily (Allyson Hannigan) and the ever-unlucky at love Ted (Josh Radnor) prep for the big event. The two-day gathering is rife with plenty of familial shenanigans and escapades as the soon-to-be-marrieds deal with problems that include Robin's disagreement with Barney's mother and brother, and Robin and Barney's holy row with the minister who is to officiate the ceremony. On the day of the nuptials, she and the gang contend with a massively hungover groom-to-be and try to concoct one of his---wait for it---legendary Stinson Hangover Fixer Elixirs. The highlight of the season is the addition of the young woman (Cristin Milioti, who was introduced in the Season 8 finale) who would become Ted's bride and the mother of his son and daughter. In the series finale, Ted tells his children the conclusion to the tale of how he and their mother finally became a couple, and the episode also offers details of what the future held for Barney, Robin, Marshall and Lily.

Marshall and Lily yearn for the luxuries of sleep and sex after the arrival of baby Marvin, while Barney tries to win the affections of both Robin and her much more intimidating father. At work, Marshall continues to strive to become a judge, and Ted tries to design his best building yet.