The privileged prep school teens on Manhattan's Upper East Side first learn that Serena van der Woodsen (Blake Lively, "The Sisterhood of the Traveling Pants") is back in town the way they learn all the important news in their lives -- from the blog of the all-knowing albeit ultra-secretive Gossip Girl.

No one knows Gossip Girl's identity, but everyone in this exclusive and complicated vicious circle relies on her website and text messages for the latest scoop. Even Serena's closest friend, Blair Waldorf (Leighton Meester, "Entourage"), is surprised to find that Serena has suddenly ended her self-imposed exile to boarding school and returned to Manhattan.

Once the Upper East Side's most notorious party girl, Serena's reasons for returning are mysterious, although they may have something to do with her younger brother Eric (Connor Paolo, "Alexander"). Whatever the reasons, the change in Serena is obvious, especially to Blair, whose friendship with Serena has always been competitive and difficult.