The JSA members gather in their projection room to view the latest newsreels, and the story that shocks them involves Texas oil millionaire John Morrison, who claims to have seen a UFO fly over and land while driving through the desert, and witnessing strange creatures as well. The Army and Police cannot find a trace, but the JSA remembers a Professor Napier from that area, and decide to visit him. They don't locate him, but a wire recorder left behind tells of the Professor building a rocketship to fly to Jupiter, so the JSA finishes the Professor's rocketship and heads toward Jupiter.; Thanks to the gravity motor, the JSA reaches Jupiter in just a few minutes, and rescues a man named Miko being attacked by the Green Star people. Miko tells them that Professor Napier is in Jovalus. Leaving Black Canary and Dr. Mid-Nite to guard Miko, the rest head for the city, being attacked by green fish men, but making it into Jovalus. Wonder Woman and Hawkman stay behind while the rest enter the city looking for Napier, where they learn that Bakeelu has a ray that can sever the Earth in two. Wonder Woman, however, has a plan in mind to thwart that possibility.; Hawkman and Wonder Woman overcome the Green Heads, then head to Jovalus, where the Flash tells them that the Conqueror got into a ship and headed for Mars, and the JSA must get to Mars as soon as possible. After landing, they attempt to find their foe and are attacked by huge ape men, who they run off. Green Lantern makes his way into the presence of the Conqueror, who offers him the chance to join him in his plan for conquest, showing GL that the other members are putting his type of helmet on and are under his control, but while GL fights against his double, the Conqueror disappears.; Bakeelu has the disintegrator aimed at Earth and ready to fire, awaiting orders from the Conqueror. The helmeted members of the JSA are told to find GL and destroy him, but the Green Gladiator uses his ring to remove the helmet and restore their sanity. They attempt to stop the disintegrator ray from destroying Earth, but it fires.....destroying the Green Star instead! Miko captures Bakeelu and returns him to Jupiter while the JSA and Napier head back to Earth in the rocketship.