Zeuglodon

A skeletal hand clutching an iron key lies hidden within a mermaid's wooden sarcophagus; a hand-drawn map is stolen from beneath the floorboards of an old museum; an eccentric sleeping inventor dreams of a locked passage to the centre of the hollow earth, and by dreaming of the passage, brings it into being... Pursued by kidnappers thinking of riches and murder, Katherine Perkins and her two cousins, junior members of The Guild of St. George, must descend into the depths of the earth in order to return the Sleeper to his ancestral home on the shores of Lake Windermere. But to awaken him would mean the end of the dream, the closing of the passage, and the three intrepid explorers marooned in a savage land forgotten by time itself...