This is the second in a two-part episode. At the end of part-two, Odo and Kira escape the foundering Defiant in an escape pod. After discovering an odd planet, Odo finds that he has found his home--and lots of other changelings like himself. For most of the episode, he hangs out here and learns to hone his changeling skills while Kira has very little to do other than to try to figure out how to contact Starfleet.
At the same time, the Dominion inexplicably has called off the war-- just when they were winning. Now folks who claim to be the Founders (they aren't) say that they love the Federation and propose a treaty with all the important Alpha Quadrant forces except for the Romulans. Things seem both too peachy and the 'Founders' are obviously not being completely honest about their intentions. After a while, Commander Sisko is furious and cannot see why the Federation is willing to work with the Dominion considering that they get nothing out of the relationship other than a chance to live, they'll unnecessarily antagonize the Romulans and they'll sacrifice everything they hold dear--such as their honor and commitment to Bajor. What gives?!
Of all the episodes of the series, this one represents the most change and flux. The changes are only beginning and what exactly is coming next is something that will slowly unfold through the course of the next few seasons. A terrific two-parter--well worth seeing.