The Ex-Files

S2 E4: When Serena notices that Dan has been cozying up to the new girl in school, Amanda (guest star Laura-Leigh), the ever-loyal Blair and her minions decide to befriend Amanda and sabotage her budding new romance with "lonely boy." Plus, Vanessa discovers a scandalous secret about Catherine (recurring guest star Madchen Amick) and enlists Blair's scheming expertise to use the information to help Nate. Meanwhile, Lily finds herself drawn back to her ex, Rufus, once again.