Ranger Clark requests aid on space station RV5. United World Secretary Drake sends Rocky Jones and the crew of the Orbit Jet to investigate. They find Argar, ruler of Medina, made a forced stop on the Forbidden Moon and was subjected to intense radiation. The only thing keeping him alive are leaves from a special plant. He limped to RV5 for repairs where his emitted radiation has put Clark in a coma. Agar grabs the working Orbit Jet and heads for his home planet. He hatches plans to conquer the universe. Rocky and his crew repair the Medina ship and give chase. They are captured on Medina and forced to do Agar's will. Agar returns to the Forbidden Moon for more plants from which Professor Newton can make a serum.
—Garon Smith