Earth officials were hard on the heels of the mysterious Sirian spy, Agent X, when he blasted off in a stolen spaceship. But before they could catch him, the master spy jettisoned the capsule that held his report into the icy rings of Saturn. In a flash, Lucky Starr and Bigman Jones found themselves in a race with the Sirian war fleet to recover it. When the Sirians couldn't find the capsule, they kidnapped Lucky…