On an alien ocean, a sailing ship is attacked by a monstrous crab-like creature, who kills and eats some of the crew before taking up residence in the ship's hold. When the surviving dozen or so crew force our protagonist, Torrin, to go below and investigate the situation, he discovers the monster can communicate and it demands to be taken to a nearby inhabited island where it plans to feast on all the residents there. After negotiating with the crab, Torrin returns above deck and shifts the balance of power when he retrieves a pistol from the former captain’s quarters. The crew deliberate on whether to obey the monster’s wishes, condemning hundreds to death, or risk their own lives to trap the crab where it can’t hurt anyone. Despite the selfish crew’s best efforts, Torrin outwits them all, eliminating one after another until he’s the only human left. When the ship finally reaches a location a safe distance from the inhabited islands, he sets fire to the vessel and escapes in the only rowboat alone.