Doctor Elefun, on his way to the moon, suddenly disappears! When Astro Boy traces the Doctor’s route in space, he finds the moon under attack by monsters from another sun! They have captured not only Doctor Elefun, but several members from Earth‘s Junior Squadron, a team of young men sent to guard the moon from just such an attack! With an electronic brain unit that transfers human knowledge to their own brains, the monsters seek to gain the necessary know-how that will enable them someday to conquer the Earth. It remains for a girl to overcome the electronic brain units in a manner so mysterious that all eyes rivet upon her! Who is this girl? Where did she come from? How does she “just happen” to know the secret of the electronic brains? A surprising turn of events helps defeat the moon monsters and re-unite the feuding members of the Junior Squadron.