1x06 The Handmaiden's Tale

Dan is torn between two girls when his childhood friend, Vanessa (recurring guest star Jessica Szohr), returns home and declares her feelings for him, just as he and Serena are trying to figure out what they mean to each other. Blair is having a masquerade party, where Nate must find her by midnight for them to consume their love for one another. Vanessa and Jenny sneak into Blair's party, and Serena gives Jenny some of her outfit - with her face hidden, she can be mistaken for Serena, which Nate does mistake her for, and kisses her, thinking Jenny is Serena. Nate does not find Blair in time.