The prelude describes a tidal wave approaching Japan. The story is a first-person narrative by Professor Katsumi, inventor of a self-programming computer which can predict the future. Katsumi and his assistant, Tanamogi, plan to predict the future of a private, individual destiny. They choose a subject from the street and follow him. The next day's paper announces his murder.

To solve the case and forestall suspicion, Katsumi downloads the contents of the man's brain, reconstructs his existence, and questions him/it. The victim did not see his murderer, but he tells the team his mistress had sold her aborted foetus for 7000 yen. Then the mistress is murdered. Katsumi's wife has a forced abortion and receives 7000 yen. Katsumi suspects an organization. His assistant Tanamogi volunteers the name of an organization experimenting with extra-utero development of foetuses, and arranges for Katsumi to visit their lab. Gradually Katsumi learns of a vast conspiracy to create an underwater nation, complete with genetically altered water-oxygenating humans and animals, bred in anticipation of the predicted destruction of Japan by a tidal wave.