Lily and Marshall worry about Lily's pregnancy, Ted and Barney ride "The Drunk Train", and Kevin proposes to Robin.
This episode provides examples of:
- Anguished Declaration of Love: The moment Kevin and Robin broke up, Ted finds Robin in the rooftop and confesses that he still isn't over her and still loves her.
- Belligerent Sexual Tension: Since Barney didn't stop complaining about Quinn, Ted realizes that Barney has fallen in love with her.
- Celebrity Paradox: Ted mentions Glee, which Neil Patrick Harris guest starred in during the show's first season.
- Continuity Nod: Robin confesses to Marshall, Lily, Kevin and Ted that she is infertile.
- Downer Ending: Robin confesses her infertility to Kevin... and he calls off the engagement.
- "Eureka!" Moment: Ted and Barney realize the reason they haven't been able to score on The Drunk Train, is that they have been sober.
- The Reveal: It turns out that Quinn did know Barney before their encounter, since she was a stripper at The Lusty Leopard.
- Romantic False Lead: Turns out Kevin was this for Robin; not having kids is a deal-breaker for him and he leaves her.
