The children return to visit their Gran and cannot wait to see Lopus and Sorren again to find out what's been happening in the Den. Lopus tells them about the mischievous fijisms and the havoc they've been causing in the Den with their enhanced magic. He desperately needs their help but there is only one creature in the Den who can solve the problem and he wants something from them in return. The children also begin to unravel the story behind the ghosts from the castle. Packed full of new creatures, follow their exciting and often dangerous adventures beneath the forest floor.