1x15 Desperately Seeking Serena

It's SAT time, and Georgina Sparks (Michelle Trachtenberg), Serena's former partner in all things bad, returns to Manhattan. They go out to a bar one night and things go haywire. The next night, they decide to have a one hour dinner, no alcohol. However, Georgina spikes Serena's drink, and she ends up missing another study night with Dan. Nate finds romance with Vanessa, the last person he would expect. Jenny meets a guy who could be her ticket to permanent popularity, but Rufus on the other hand, grounds her for the Valentino incident. Dan and Blair discover Vanessa and Nate are spending time together.

Meanwhile Blair is trying to bring down Nelly Yuki, one of the smartest girls at Constance, so that she will wipe out the competition for Yale. She does so by keeping Nelly off focus by having her ex-boyfriend mess with her feelings so that she will screw up her SAT's.