Following a mysterious disappearance, Serena Van der Woodsen suddenly returns to the Upper East Side from boarding school to visit her suicidal brother, Eric. Blair Waldorf discovers Serena had slept with her boyfriend, Nate Archibald, the night of her disappearance. Meanwhile, Brooklynite Dan Humphrey and Serena begin dating while Nate struggles with his feelings for Blair. Nate and Blair try to salvage their relationship, driving Blair to lose her virginity to Nate's best friend, Chuck Bass. Jenny Humphrey, Dan's sister, is trying to fit in to the Upper East Side by following around Blair and her friends. Vanessa Abrams, Dan's best friend, returns. It is revealed that Dan had confessed his love for Vanessa in the past, but the two move beyond this as friends. It is discovered that Lily Van der Woodsen, Serena's mother, and Rufus Humphrey, Dan's father, have a romantic past and begin to rekindle their romance but decide to see other people in light of their children's romance. Blair and Nate eventually break up, after finally having sex. Nate discovers Blair's affair, causing a rift with Chuck. Throughout the season, Chuck tries to seduce Blair and the two somewhat come to terms with their feelings for each other. Georgina Sparks, past friend of Serena, returns, pretending to be a woman named Sarah from Portland. Georgina's return reminds Serena of the real reason she left the Upper East Side. It is revealed that Serena left the Upper East Side because she was involved in a drug-related death and felt responsible for the situation. Problems erupt between Dan and Serena, as Serena tries to hide her secret from him. However, the incident is resolved with Serena being absolved of her guilt and Georgina leaves. Dan and Serena decide to end their relationship. Meanwhile, Lily accepts a marriage proposal from Bart Bass, despite her feelings for Rufus, and the season ends with a Bass wedding and Blair waiting for Chuck at the airport.