A new phase in the never-dull life of Bernice Summerfield opens as she arrives on the human colony world of Maximediras, with her son Peter in tow, to begin work on a much-needed freelance assignment. Relics from a hitherto unknown civilisation have been discovered on the sea bed and Bernice has been hired by the planet's tourist board to travel out on one of their cruises and undertake a survey. What is causing this? Or who...?