Once again, we discover that Clarke can write.
Again, as in others of his works, the heroes are not Earthmen ~ though descended from human genotypes, they are native Thalassians, and have been for generations. The Earthmen, the last in the universe, appear in the spaceship Magellan (no symbolism there, is there?), on their way to another star system, hundreds of years away, and it becomes doubtful ~ briefly ~ whether they will play the part of antagonists or behave themselves and fulfil their mission. The true antagonists, though, that will in generations to come challenge the Thalassians, are a previously unknown true native (not from Earth genotype) of the oceans of Thalassa.
Clarke’s imagination, knowledge, and ability to guess ~ accurately ~ where he does not know, is, as always, phenomenal. The picture of a colony of humans on a planet of water, struggling for survival in what could be a harsh environment, since it is not the original of their genotype, is brilliant. Though they struggle, they also live indolently, like the original South Sea Islanders, obviously the source of much of the picture. Yet there is something wonderful and scary in the idea of their founders ~ the Earth scientists who created their Mother Ship, loaded it, sent it ~ choosing for them the form of their culture, the portions of history, literature, Art, that they would have access to. The Thalassians are truly not Earthmen, for they do not have the history of Earth behind them. What we are shown is what a culture of humans would be like without Earth. Interesting idea.