Just a few weeks after his sensational return from the City of Rainmakers, Karl Friedrich Donhauser, who calls himself the son of the great naturalist Wilhelm von Humboldt, takes on a new business. He and his faithful companions will have to find in the Aegean Sea the reason for the mysterious disappearance of several dozen ships. To achieve this goal, Donhauser-Humboldt charters the Calypso, the most modern research vessel of its time, and the world's first bathysphere, a deep-sea diving device that allows you to spend several hours underwater. However, the scientist and his companions have to spend much more time on the seabed than they expected - at a depth of over two hundred meters they make an incredible discovery...