The two main events in this hour were Dan and Serena's first date; and Blair's big sleepover. On the same night, of course. Because S is missing the event, B invites Jenny in her place. But her intentions aren't exactly benevolent; Blair is basically set on initiating Jenny throughout the evening.
First, though, let's head over to Dan and Serena's date. It doesn't begin well because our boy thinks he has to impress Serena with some fancy meal. Doesn't he realize she's looking for a Dan Humphrey date? Once she makes this known, the adorable pair end up at a pool hall. They're about to kiss when Dan's phone rings. For what reason?
We'll recap it: during a dangerous game of Truth or Dare, Blair dares Jenny to break Eric out of the recovery center. Pressured and wanting to be accepted, Jenny (or "little Humphrey," as Blair dubs her) accepts the challenge. Her and Blair pull a fast one on the night nurse and get Eric out of his room... and into an upper class bar, in order to continue with the sleepover.
This is where the phone call to Dan comes in: See, the treatment center called Lily and said Eric was gone. Lily thought he was with Serena, who was with Dan. So she called Rufus (who earlier had found out that his wife is now living with another man), who called Dan eventually found out the truth: that Eric was actually with Jenny and Blair at a bar.
The scene there is sort of a mess, as Blair and Jenny get in trouble with a guy and his girlfriend. Dan doesn't understand what Jenny is doing, but she assures him that she won't lose track of who she is as she hangs out with Blair. Dan says okay, as he leaves to walk Eric back to the center with Serena.
During this entire time, Rufus and Lily are bonding at his apartment, waiting for the call from their kids.
The episode ends with: Lily telling Eric he can come home; Jenny talking her way out of a breaking and entering charge that Blair had tried to stick on her, thereby earning Blair's respect; and Dan and Serena kissing. A lot.
(Source: TV Fanatic)