We have seen Hermione for years from only Harry's perspective. A lot can happen in the time he wasn't around. A hidden relationship perhaps? Hermione is the brightest witch of her time she could easily hide a whole relationship. Even if that relationship happened to be with Draco Malfoy. It's the same story we all know and love. Only now we get to see their relationship slowly progress from enemies, to friends, to lovers and to complete strangers. We get to see that not all epic love stories have to last forever.
8 parts