S5, E7: Several of our favorite Upper East Siders attend a performance of Punchdrunk's provocative theater experience "Sleep No More," which means masks, anonymity and some surprising romantic twists by the end of the evening. Meanwhile, Diana (recurring guest star ELIZABETH HURLEY) sets her sights on Serena in her quest to ruin Gossip Girl. Plus, Dan is out on his book tour, but things aren't exactly as they appear to his friends and family.