A violent explosion in space touches off one of the most thrill-packed adventures in Tom Swift Jr.'s scientific career. The appalling news that a cargo rocket has disintegrated while en route with vital supplies to Swift Enterprises' research base on the asteroid, Nestria, sounds a grim warning that the lives of Nestria's personnel are at stake.

To rescue the marooned men, Tom undertakes a hazardous voyage to Nestria, only to find the way blocked by an invisible barrier of deadly radiation created by an unknown enemy whose objective is possession of the base.

Tension mounts at Swift Enterprises when a mysterious Oriental is shot while attempting to warn Tom that his life is in danger from the Black Cobra. The Oriental's mumbled warning, plus some revealing data collected by United States Intelligence, sends Tom winging to a secret fortress in South America for the first encounter with his inscrutable foe.

But the decisive encounter is destined to take place in space. How Tom uses his new invention, the magnetic deflector, to crack the radiation barrier around Nestria, and how the young space scientist and his crewmen pit their wits and courage against the asteroid pirates and their diabolical leader, the Black Cobra, will hold every reader breathless with suspense.