Marshall suspects that he is the reason Lily can't get pregnant after meeting a fertility doctor who also happens to be Barney's doppelganger. Meanwhile, Robin's embarrassing past is revealed at work by her former co-anchor.
The gang tries to support Marshall and Lily tries to help his mom during Marshall's father's funeral, but Marshall becomes preoccupied when he discovers that he has one final voicemail message from him.
Ted discovers that he is in love with Zoey after she tries to set him up on a date with her naive cousin, and he cuts off their friendship as a result. But little does he know that her marriage status has changed and she loves him too.
Lily goes to Minnesota to bring Marshall back, but he's not ready to leave yet. Meanwhile, Ted and Zoey's relationship gets off to a rocky start, and Barney searches for a female "victim" the night before Valentine's Day.
The Captain asks Ted to help find out who stole Zoey away from him, Marshall withholds sex until he does something to help the environment, and Barney is reluctant to admit that he has a crush on Robin's friend.
Despite Zoey still opposing the new GNB headquarters being built on the Arcadian Hotel site, Ted and Zoey's personal relationship is thriving. That issue is only one of the many disagreements in their life, which Ted likens to the two challenging each other mentally. On the other hand, he sees Marshall and Lily's relationship as being boring, as they agree on everything to the point of them almost melding into one person. Lily and Marshall, on the other hand, see their relationship as being supportive, the way that relationships should be, whereas they see Ted and ...
When Marshall switches sides on the Arcadian dispute, his friendship with Barney is compromised and the gang is banned from the bar. Meanwhile, Ted finally finds the courage to confront Zoey about the same topic.
In the aftermath of Ted and Zoey's break-up, Ted is having second thoughts. He is freaking out about an issue with the GNB headquarters, and historically when Ted freaks out about something, he turns to dating an old girlfriend if only for something comfortable and familiar, however bad returning to that relationship ended up being. When Barney and Robin find out that Ted is going to meet Zoey to get back together with her, they have to try and figure out where that meeting place is so that they can stop him. Beyond piecing together this puzzle, Barney and Robin's ...
While Barney prepares for his wedding to a mystery bride, he and Ted reminisce about Punchy's wedding, including when Marshall and Lily announced they were having a baby. Meanwhile, Robin considers telling Barney she has feelings for him.
Robin tries to date her therapist, Marshall thinks his boss has gone soft on environmentalism, Barney suspects that Nora may be lying about her age, and Ted takes his Intro to Architecture class on the worst field trip ever.
Ted agrees to go on a date without researching her on the Internet beforehand; Barney urges Marshall and Lily to find out and reveal the gender of their child; and Kevin tries but fails to avoid passing judgment on the group.
Kevin's declaration that everybody marries their parents ruins Marshall and Lily's romantic evening, but will anything keep Barney from getting lucky with Nora? And will Kevin finally get fed up with Ted and Robin's close relationship?
Ted finds his long-lost crush from a Halloween party 10 years ago, but will there be any chemistry? Meanwhile, Lily's "pregnancy brain" convinces her to move to the suburbs, and Barney finds out he's one-quarter Canadian.
The gang explains to Kevin the origins of the "No Boogie-Boarding" sign in front of MacLaren's, which has to do with Hurricane Irene. Meanwhile, Barney negotiates with Marshall about how to get out of wearing the ducky tie.
After Robin tells Barney that she's pregnant with his child, she receives some shocking news from her doctor. Meanwhile, a neighborhood teen plays a trick on Marshall while he decorates his house with Christmas lights.