Angus, a young boy living in WWII Scotland, has grown more and more reclusive since his father went off to war. During a solitary search for sea shells on the beach, a pastime he shared with his father, Angus finds a mysterious object on the shore. Uncertain of its origin, he takes it home, hiding it for safekeeping. However, when it hatches overnight, he finds himself the proud but puzzled caretaker of a water horse - a sea creature of mythic proportions.