After Marshall sees a documentary about garbage, he becomes fixated on saving the environment. Meanwhile, Ted runs into Zoey's ex-husband, The Captain, and Robin forces Barney to admit he has feelings for Nora, the girl who made history as his first Valentine's Day date ever.

When Barney finally meets his father, he's surprised to learn how his life turned out. Meanwhile, the gang points out each other's "gaps," something they should know by adulthood but never learned.