Barney declares February 13th a holiday for desperate women. Marshall receives a Valentine's Day surprise from Lily. Zoey and Ted work on figuring out their relationship.

Marshall becomes obsessed with saving the environment after seeing a documentary on garbage. Ted runs into The Captain. Barney admits he has feelings for a woman.

When Barney starts to have real feelings for Nora, he worries that something is wrong with his heart. Meanwhile, Robin starts dating a guy who acts a lot like a dog.

Robin and Barney bond when they intervene in Ted's relationship, and Marshall and Lily watch a ticking clock as he fears that he soon will be the victim of food poisoning.

Marshall gets a great job offer that he fears may be scuttled by a social media background check. Ted needs a date for the Architects Ball.

After Robin assaults a girl who is out to ruin Barney's relationship, she is forced to begin court-mandated therapy sessions. Meanwhile, Ted gets too involved in Lily's pregnancy.

Marshall decides to step in after seeing his boss's approach to settling with a million dollar company. Ted's class trip isn't what he envisioned.

The gang begins to realize their romantic partner reminds them of one of their parents. Meanwhile, Barney and Nora's planned romantic evening is ruined by a string of bad events.

Barney and Robin are afraid to break the news to Nora and Kevin that they cheated with each other and want to get back together, while Ted and Marshall get stoned together at a concert.

In an attempt to deliver a devastating final slap to Barney, Marshall explains how he mastered the Slap of A Million Exploding Suns.