The Legion of Super-Heroes have to go to Doctor Mantis Morlo's lab to stop his experiments, because his experiment is causing poisonous radiation. Dr. Morlo refuses and sends his Chemoid robot to fight the Legion, but the Legion defeat him and stop Morlo's experiments. Soon, Princess Projectra is summoned to her planet of Orando because there's a black cloud surrounding her planet. She brings her fellow Legionnaires to help out and they reveal that it is Dr. Morlo behind this mess.