The Moon, which has been orbiting the Earth for millennia, is an artificial satellite built by the Creators, a highly advanced race of space roamers who use the planets as industrial bases or incubators for growing biological organisms of many different types. A long time ago, such an incubator existed on Earth. But something did not suit the Masters, and they left this sector of the Galaxy forever, leaving unattended the bioorgs that had bred on the planet and the ownerless station dangling above their heads, considering it unnecessary to destroy absolutely everything. Russian cosmonaut Semyon Lisitsyn will find out about this by visiting the bowels of the Moon, ships of the Creators and other planets.