Tizzie, aged nearly 11, and Louis, aged seven-and-three-quarters, are on holiday in Cornwall when they enter Echo Cave and are transported through the Crystal Pool to the amazing and mysterious Kingdom of Kernowland in Erthwurld. Kidnapped by the nasty Melanchol Drym to be sold as slaves to Captain Pigleg and his pirates, they are soon separated in a slave auction at the Polperro Inn. Their plight looks hopeless.... until Louis is helped by the kindly Mr. Sand. He discovers Tizzie is being taken to Jungleland, to be used as bait for Big Red Grunter, a huge, mutant, child-eating, wild boar. Now, before they can go home, the young boy has to rescue his sister. And so their adventure in Erthwurld begins....