S6, E6: Blair gets ready for her mother's (recurring guest star MARGARET COLIN) imminent arrival, but is unprepared for the set of demands her mother puts upon her. Serena volunteers to help Dan find a new place to live, but their time together brings up unexpected emotions. With Ivy's help, Chuck discovers there is evidence incriminating his father in illegal activities and enlists the help of Nate to retrieve it. Meanwhile, Rufus and Ivy are excited about their art gallery opening until they find an empty RSVP list and must scramble to find another way to make the event a success.