Secret Enemy

Astoria's whole family was Sorted into Slytherin; why does the Hat consider placing her in Gryffindor or Ravenclaw? Over the course of her fifth year at Hogwarts, she learns why she's not a typical Slytherin. After all, typical Slytherins don't sneak out in the dead of night to post anti-Carrow messages on the chalkboard and call themselves the Secret Enemy. Set during DH.