Time after time, mysterious forces destroy the huge underwater dam being built by the Institute of Science. Why should anyone wish to destroy it? How do these forces create the irresistible whirlpool that no dam in the world could withstand? Astro Boy’s underwater investigation unearths a surprise; the whirlpool is created by an enormous bed of oysters! Not Earth-bound oysters, but oysters that traveled here from a doomed planet. Trouble at home meant destruction of that planet; and so the oysters – actually a kind of flying saucer operated by tiny Pearl Men who lived Within – had migrated to our waters, closest to their Own. All they wanted to do was rest on the ocean bottom until they could return to their own planet, but the constant construction noise from the dam site kept them awake. And so every time the noise became too great, the Pearl People agitated the water into a Whirlpool. Astro Boy learns the simple explanation too late to stop the barrage of Starfish Depth Charges from above. All his persuasive skill and unabridged strength are required to abort the attack and launch the Pearl People safely on their long voyage home.