1.17 "Woman on the Verge"

Serena falls back into her old habits of drinking and drugs. She eventually reveals to Blair true reason why she left Manhattan: to avoid being implicated in an accidental drug overdose of a school friend in which Georgina was also present. Blair, Nate, and Chuck are forced to team up to try to help Serena deal with this situation. Unfortunately, Serena is too ashamed at herself to share the truth with Dan about her mistake, and therefore he naturally assumes the worse about his girlfriend. Lily discovers the blackmail videotape Georgina made showing her and Serena that night with their victim. Being who Lily is, she too jumps to the wrong conclusion about Serena and it takes a little intervention from Blair to save her friend from being emotionally torn apart for good. Blair also discovers from Vanessa that Georgina, under her alias 'Sara', is still hounding them by pretending to be their friends, and Georgina takes advantage of Dan's alienation with Serena to make the moves on him. Meanwhile, Rufus is excited when his band is invited to perform at a Rolling Stones sponsored concert. But Lily is the last person on Earth he expects to see at the performance, especially since her wedding rehearsal dinner is on the same night.