Mister Monday — Garth Nix

Arthur Penhaligon is not supposed to be a hero. He is supposed to die an early death. But then his life is saved by a key shaped like the minute hand of a clock.

Arthur is safe - but his world is not. Along with the key comes a plague brought by bizarre creatures from another realm. A stranger named Mister Monday, his avenging messengers with bloodstained wings, and an army of dog-faced Fetchers will stop at nothing to get the key back - even if it means destroying Arthur and everything around him.

Desperate, Arthur escapes to the mysterious house that has appeared in town - a house that only he can see. Maybe there he can unravel the secrets of the key - and discover his true fate.