Impossible Creatures by Katherine Rundell

About There's a place where all the wildest stories began … From Katherine Rundell, winner of the Costa Children's Book Award, the Blue Peter Book Award and the Waterstones Children's Book Prize comes the first novel in a landmark trilogy for 9+ fans of His Dark Materials

Christopher is stunned when he discovers a passage to the Archipelago: a cluster of magical islands where all the creatures of myth still live and breed and thrive in their thousands. There he meets Mal: a girl from the islands, who is in possession of a flying coat and a baby griffin, and who is being pursued by a killer. Together they embark on an urgent quest to discover why the creatures are suddenly perishing, voyaging across the wild splendour of the Archipelago, where sphinxes hold secrets and centaurs do murder, in a bid to save both the islands and the world beyond them from a rising evil – before it's too late.