Consternation and panic grip the world as a strange new moon shoots earthward. Millions of people are relieved when the weird, glowing runaway moon in the sky finally goes into orbit 50,000 miles from earth.

Tom Swift Jr., who has developed a machine that will produce artificial earth-type gravity in the airless void of space, makes plans to explore this new satellite. In the gigantic, atomic spaceship Titan, Tom and his associates land on the mysterious moonlet and claim the bleak but fabulously rich possession for the United States.

While exploring the satellite to pinpoint the best location for setting up the young inventor's atmosphere-making machine, Swift expedition scouts discover a spaceship belonging to a hostile nation. Claiming first right to the moon because of prior landing, the foreign scientists try every means to annihilate Tom and his group.

How Tom succeeds in proving the Brungarian claim invalid, and saves his associates from being set adrift in outer space, will keep the reader spellbound to the very last page of this spine-tingling adventure.