When sailors aboard a Dutch ship in 1663 spot a man, tangled in a net, they row the rescue boat to him. But when they bring him into the boat, they discover they have captured a creature, half man and half fish. The superstitious crewmen want to kill it, afraid it will bring storms and bad luck. But Lieutenant Huiskemp and Pieter the cabin-boy believe the creature is part of creation and deserves to live.