Balloons and streamers? Carvel cake? Those might be standard fair for your average birthday party, but Whitney Blake and Sophie Mitchum are anything but average. I'm Laura Finnegan - thrift store junkie and scholarship student at Tate, our posh all-girls high school in Manhattan. I'm not like Whit or Soph, but that doesn't stop us from being BFFs. But then they started tuning in to the all-Sweet Sixteen, all-the-time channel. Now tempers are flaring,...