Shapeshifter

Louis is a Shapeshifter and Harry is a Vampire. Niall is a Vampire. Liam is a Vampire. Zayn is a human.
Harry and his pack are on the run from the Werewolves hunting for his pack and they all find shelter alone. Harry finds himself sneaking into a mansion and almost attacked by a guard dog.
Harry convinces the human, Zayn, living in the mansion to let him stay and after many confusing days he finds out the dog, wasn't a dog.

Sorry, I suck at summaries, basically Zayn is Louis' best friend and Zayn's personal Shapeshifter/guard thing.