405 - Nowhere Man
Well, that was fast. Suddenly every secret that the characters have been holding onto throughout the season comes out all at once. I'd forgotten how quickly HaCF burns through plot points that a lesser show would stretch out over half a season or even longer. Throw in Bos and Donna's fight followed by his collapse, and a killer PJ Harvey montage at the end, and you've got another strong episode.
(Also Tom was there for a while too, but no one likes Tom.)