CBS released another press release, this time for the episode following ‘Desperation Day’ and this one is called “Garbage Island”. Here is a little info on it.

MARSHALL BECOMES OBSESSED WITH SAVING THE ENVIRONMENT AND TED RUNS INTO ZOEY’S EX-HUSBAND, THE CAPTAIN, ON “HOW I MET YOUR MOTHER,” MONDAY, FEB. 21
“Garbage Island” – 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, on HOW I MET YOUR MOTHER, Monday, Feb. 21 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Nazanin Boniadi (“General Hospital”) guest stars as Nora.