Welcome to New York's Upper East Side, where the claws are about to come out! Blair and Serena were BFFs...until Blair discovered that her boyfriend, Nate, cheated on her with Serena! As if that wasn't enough, Serena then disappeared without a word. Now she's back and trying to make amends with Blair. Too bad Serena's former best friend has no intention of forgiving her. After seeing Serena with her new boyfriend, Dan, Blair intends to respond in kind! How far will she go to make a mess of Serena's life?