In this sequel to Hal Clement's "Mission of Gravity" human beings have recruited Barlennan and a host of Mesklinites to explore another massive planet named Drawhn. Unable to withstand the planet's extreme gravity, the human beings stay aboard a space station 6 million miles from the planet. While exploring the surface of the planet in a specially designed ship, a group of Mesklinites are surprised by a flash flood which strands them thousands of miles away from their base. The humans, back on the space station, do their best to help, but are unaware of everything the Mesklinites are up to on Drawhn.