In medieval Japan, in a coastal village where the ramshackle houses are blasted white by the salt winds, a father sells himself into indentures servitude to save his family from starvation.

He leaves the responsibility for the family's continuing survival with his nine-year-old son Isaku. Forced to grow up well before his time, Isaku must learn quickly to trap saury fish and to distil salt; and is faced with a number of mysteries, not least his nascent sexuality and the legend of O-fune-sama - of ships wrecked offshore, providing the village with unexpected bounty.

As the end of his father's bondage approaches, and another ship founder on the rocks, Isaku and villagers rejoice. But the cargo is not at all the manna of their hopes. At first mystifying, then terrifying, this cargo is about to change their lives forever.