第 4 季，第 19 集: Serena enlists Charlie (recurring guest star KAYLEE DeFER) to go undercover, Gossip Girl–style, to determine why Dan and Blair are spending so much time together and what role an unexpected visitor is playing in their lives. Meanwhile, with Nate's help, Raina (recurring guest star TIKA SUMPTER) decides to go on a search for her long-lost mother, and Chuck's hopes about his legacy are dashed with the reveal of devastating information from the past.