S2, E17: In retaliation for her teacher, Rachel (recurring guest star Laura Breckenridge), not playing by the unspoken rules of Constance Billard, Blair comes up with a plan to bring her down. After Chuck wakes up in a hotel and only has a minor recollection of what happened the previous evening and who he spent the evening with, Nate and Vanessa try to help him fill in the missing pieces of what is turning out to be an increasingly intriguing mystery.