The owner of six lead mines on the moon Planos reports that an epidemic is spreading through the mines. Berger, the owner asks for assistance from the United Planets. Commander Corry, Tonga and Cadet Happy are dispatched on a rescue mission with the needed serum to halt the disease. However, Burger and his assistant are trying to keep quiet a secret discovery of a rich deposit of Exonium. Captain Happy discovers Leckner tampering with the atmospheric controls in one of the mine shafts. In a struggle with Cadet Happy, he unknowingly inhales a lethal dose of the concentrated bacteria.