Impossible Creatures, by Katherine Rundell

Magical beasts once populated the world but they are now hidden away in the Archipelago, a group of secret islands. Christopher has always had an affinity with animals and when he visits his grandfather in Scotland he discovers he comes from a line of gatekeepers to the magical world. Mal lives in the Archipelago with her great aunt and she is worried about a creeping influence that seems to be draining the magic from the land, putting all the creatures at risk. When an assassin threatens Mal she recruits Christopher to the cause of saving the Archipelago. They are helped on their difficult and dangerous quest by a Berserker and a marine scientist, as well as some of the magical creatures they are trying to save. Griffins, centaurs, dragons, unicorns and nereids are amid a plethora of less familiar creatures that are difficult to keep track of, despite the helpful guide at the start of the book. Power, sacrifice and conservation are strong themes in a book aimed at older children and Rundell pulls no punches in this rather violent adventure tale.