An unidentified rocket ship crashes into the Swifts' outpost in space and vanished before Tom can track it down.

Shortly after comes the startling news that a Mars probe rocket, vital to the United States space program, has failed to respond to signals to bring it back to earth. Tom is confident that with his latest invention -- the Polar-Ray Dynasphere -- he can retrieve the stranded missile. But a web of espionage threatens his plan. A clue to the solution of the mystery prompts Tom to accept an invitation from the young Prince Jahan to visit his native land of Vishnapur in the snow-peaked Himalayas north of India.

In this remote Oriental kingdom, Tom and his pal Bud Barclay visit a strange lake of death and sight the tracks of a weird monster said to prowl the lake at night. Tom conceives an ingenious plan for draining the poison lake with the Dynasphere mounted aboard his new spacecraft, the Dyna Ranger, so that the valley may be turned into valuable farmland.

Fireball missiles and a hairbreadth encounter with a charging tiger are only two of the perils that confront the daring young inventor in this colorful, thrill-packed adventure.