The hero of the animated film is Pepolino, a singer who becomes a sailor to search for his lost grandfather and his immeasurably valuable treasure. During the adventurous voyage across the seven seas, his greatest enemy is the witch Hildegard, who sets the pirate trio Red Beard, Peg Leg and Glass Eye on him. The money-hungry Captain Babaluk also gives him a hard time. But he finds loyal and brave friends in Jakob the dog, Poch the parrot, Emil the ship's rat and Babette the cat. And when he meets the mermaid Mora, he also finds true love.