Season 1 - Episode 6

6 - The Handmaiden's Tale
Dan's childhood friend, Vanessa returns from home, declaring her feelings for Dan. Blair holds a masquerade ball, and although no outsiders are allowed, a disguised Jenny - with the help of Vanessa - and Dan arrive - taking the identity of some drunk boy. Blair sends Nate on a scavenger hunt on which he is distracted from by Serena, who is actually Jenny under a mask, whom he gives a kiss to - thinking it is Serena. Meanwhile Lily takes Rufus to an Eleanor Waldorf event to make Bart Bass jealous.