As his 31st birthday nears, an all-nighter to try to get business has Ted realizing he may need to pursue another career than architecture. Meanwhile, Marshall tries to get him up to a rooftop surprise party.
Ted continues trying to land a client for Mosbius Designs, and when Tony tries to help nothing goes as planned—for either of them. Barney tries to smooth talk his way out of a ticket.
Ted explains to his future kids how a series of unrelated events led to a chance encounter with a former girlfriend. Barney makes the 200th notch in his bedpost. Marshall goes overboard when he discovers GNB has a department that can make him charts and graphs.
When Ted violates the ‘three days rule’ by continually texting with a girl he’s just met, Barney and Marshall retaliate by impersonating her.
Ted goes out on his own as an architect and hires an intern to help get things started, but all he helps himself to is Robin. Meanwhile, news of impending layoffs at GNB has Marshall looking for a schtick to make him indispensible.
Barney attempts to complete in a single day all the tasks from a list Ted made to prove the gang’s not too old to do them. Meanwhile, he challenges Ted to complete a list of things they’re too young to do yet.
Marshall and Barney lie to keep Ted from finding out the headquarters he’d been hired to design for GNB has been cancelled. The gang try to decipher the story of a celebrity encounter Robin once had.
Ted is shocked to learn that Lily is responsible for many of his breakups with ex-girlfriends-including Karen. Meanwhile, Marshall defends his wearing of a nightgown to bed.
Ted’s college girlfriend reenters his life and leaves Marshall and Lily remembering how much they hated her, while Barney tries to steer the storytelling towards Marshall’s forgetting his pants at work that day.
Suspecting he has a secret girlfriend, the gang follows Barney when he leaves MacLaren’s and discovers he seemingly has been keeping a family secret from them.