Isaku is a nine-year-old boy living in a remote fishing village on the coast of Japan. To survive, his people distill salt to sell to neighboring villages. But this industry serves another, more sinister purpose: the fires of the salt cauldrons lure passing ships onto rocky shoals. When a ship runs aground, the villagers slaughter the crew and loot its cargo for rice, wine, and other goods. One day a ship founders on the rocks - but Isaku learns that its cargo is far deadlier than could ever be imagined.