He-Man and Man-At-Arms set sail to investigate the disappearance of some of King Randor's food ships. Sucked beneath the surface by a whirlpool, they find themselves in the underwater city of Aquatica, which has been taken over by Merman. Merman has kidnapped the city's princess, Nahmi, and is controlling the Aquaticans with the Pearl of Power! But he has convinced them that the surface dwellers kidnapped Nahmi, and the Aquaticans have waged war against the people of the surface. Can He-Man help the Aquaticans see the light, and rescue Princess Nahmi before Merman creates more havoc?