Christopher is visiting his reclusive grandfather when he sees an avalanche of mythical creatures come tearing down the hill. This is how he learns that his grandfather is the guardian of one of the ways between the non-magical world and the Archipelago, a cluster of magical islands where the creatures we tell of in myth live and breed and thrive alongside humans. They have been protected from being discovered for thousands of years; now, terrifyingly, the protection has worn thin, and creatures are breaking through. Then Mal appears in Christopher's world. She is in possession of a flying coat, is being pursued by a killer and is herself in pursuit of a baby griffin. Mal, Christopher and the griffin embark on an urgent quest across the wild splendour of the Archipelago, where sphinxes hold secrets and centaurs do murder, to find the truth - with unimaginable consequences for both their worlds.