"Someone has stolen your invention!" Bud Barclay tells his pal Tom Swift Jr. And when a scientist in France publicly tests a helium-extraction machine, it seems Bud is right. The machine explodes, precisely as Tom predicted any model made from his own unperfected plans would do. But the explosion is only the beginning of one of the strangest mysteries in the young scientist-inventor's career. Time and again he is forced to combat a sinister secret enemy while he works to complete his megascope space prober, designed to "keep an eye on the universe."

Meanwhile, Bud is offered the opportunity to participate in a manned government space probe to Venus. Although the AstroDynamics Corporation, a competitor of Swift Enterprises, is directing the project, Tom encourages his friend to make the flight in the interest of the United States.

When another secret invention of Tom's becomes the target of his enemy, all evidence points to the fact that an unidentified traitor at Swift Enterprises is in league with a criminal mastermind outside the plant.

How Tom is trapped when he unmasks his enemies, how he engineers a bizarre escape, and how he executes a fantastic rescue when Bud's spaceship goes out of control on its flight to Venus are just a few of the suspense-filled highlights in the young space pioneer's latest challenge.