As the Legion attempts to evacuate the planet Mordan before its star goes nova, they are confronted by the Fatal Five, who want the inhabitants of Mordan to be converted into priceless energite when their star explodes and have taken Karate Kid and Princess Projectra hostage to make sure the Legion doesn't interfere. And, after delaying the Legion's efforts to save the inhabitants of Mordan, the Fatal Five regroup on Tharok's ship. The Legion mounts a sneak attack on the ship and tricks Tharok into revealing the location of the control for the device causing the star to go nova.
The High Seer of Naltor has a prophecy that the sun of the planet Mordan will explode into a super nova in mere hours. The United Planets get the aid of the Legion of Super-Heroes to evacuate its citizens before they die. Meanwhile, the Fatal Five make a return in this unfortunate time. The Legion defeats them and is able to save the planet of Mordan from destruction.