Lake Wanuka lies in a deep bowl between the Heidelberg hills. It has neither tributary nor source, and its depth has never been measured. Geologists say that when the Great Glacier melted, its waters filled an incredibly deep depression here. This was fifty thousand years ago. Beneath the calm surface of the lake lies another world inhabited by little people. These people live forever and do not know what illness and death are. Previously, they solely owned the Earth and now they want to take it back. Archaeologist Hugh Lambert finds himself drawn into the serene depths of the lake and learns of a sinister plan to conquer the Overworld.