Book is anti-whaling novel which uses sick cetaceans to transmit a pathogenic virus to humans. The virus combines with another virus and kills most of human population. Some of the elite population goes underground and eventually causes a problem for the ones who did not go underground. Novel consensus by the book's heroine virologist is that the world was created to stop overpopulation by any one species and that humans are due to be thinned out. Some are spared by having been near the sea and picked up an archea virus, some are spared completely due to a virus passed down through the reptile line, and some change marginally according to their degree of association with the sea. The novel establishes a logical and appealing reason for mermaids and uses Australia as a venue. Changelings inter-marry and have offspring that will not change, but will be the new builders of human culture. Surviving humans are given the chance to be better and build anew. The final outcome is explained to the heroine by an old Australian aboriginal.
