How I Met Your Mother

The Mermaid Theory

Aired Dec 6, 2010 · 8:00 PM ET · 25 min

When Ted's new friendship with Zoey tests the theory that single men and married women can't be friends, he invites her husband, "The Captain," to hang out with them. Meanwhile, Marshall and Robin decide to spend alone time together, and Barney and Lily possibly have a fight.