Synopsis: From the front flap of the Walker edition: "A tanker is sunk in the Atlantic. It comes to rest on a shelf of rock not far below the surface - somewhere. There are five survivors, two women and three men, one a doctor. The hold in which they have taken refuge is watertight and not too uncomfortable. There is plenty of food. Light, wather and oxygen are all available. They live. The world outside passes them by. In time the multiply. Deep in space the last remnants of a great people are in helpless flight from their dying planet. The Unthans are water-dwellers and their sun has grown too hot to support life. But the deep-freeze system, hastily designed to allow them to live until their destination has unexpected flaws. The crew must stay awake - and age. Time passes. They multiply. At last their destination approaches - Earth. In the tanker, generation has succeeded generation but now it seems that the end so long postponed is at hand. The food supply is nearly exhausted. The tanker walls are rusting. Already some compartments have been abandoned to the sea. The handful of survivors resign themselves resentfully to extinction. In the oblivious world above, all is confusion. The Unthans have landed - and have disappeared into the depths of the sea. How hostile are these mysterious invaders? What can be done to combat the threat they pose? Now is the moment of destiny for the tanker people. They alone, with their unique experience, can provide a bridge between the aliens and their own people who are in many ways so much more alien. The common experience of generations - will it prove enough to permit a working relationship between two races so utterly dissimilar?"