Well Between The Worlds — Sam Llewellyn

The land of Lyonesse is sinking, and the sea batters its walls; it has become a place of poison and danger, and its people live in an uneasy truce with the monsters that inhabit its bottomless Wells.

Idris Limpet is an ordinary boy, until the day he is rescued from a terrible death and finds himself thrown into an astonishing new adventure. Can it be that it is his destiny to save Lyonesse? As Idris begins to discover his true self, he learns he must rely on his wits, his courage, and his friends in the face of an overwhelming darkness that threatens to swallow up everything he loves.