In a future where relations between Japan and China are growing strained, the pride of humanity is Ocean Techno Polis, an artificial city afloat on the sea. Then an unexplained disaster strikes, first wrecking a Taiwanese submarine and then taking down the whole city. Kurase, one of the engineers who works on Ocean Techno Polis, has to hurry to save his family. On the way he runs up against a Japanese navy determined to guard its own secrets, and he must find out what sent the city to the ocean floor. The science fiction film adapts a 1995 novel by Katsufumi Umehara.