Astro Boy and his pal Specs visit a carnival fun house where Specs is frightened by all the tricks played on them. But Astro Boy has no fear because as a robot he lacks a human heart. He longs to learn what fear feels like and so he persuades Doctor Elefun to give him a human heart for a few days. Doctor Elefun reluctantly gives Astro Boy the heart and then leaves by ship on a long ocean voyage. Astro Boy is taunted by his sister about his new fears. They overhear sailors talking about a dangeroUs haunted ship in the ocean near where Doctor Eiefun’s liner will be passing. Astro Boy overtakes the doctor’s ship and tries to have the captain turn back. But the captain refuses. Astro Boy is sent ahead to keep watch for the haunted ship. He finds it and on board he battles huge mutated plankton. He almost loses the fight and then his human heart stops and once again he is Astro Boy the fearless robot. He defeats the plankton, and then Weezzell and his gang, who have been using the haunted ship as a decoy while they transport uranium by submarine beneath it. Astro Boy wins and saves the liner. And he has learned that he is happier without a human heart, and without fear.