A weird blast of sound engulfs an American city. Tom is caught in the panic while visiting there to demonstrate his new sonic boom deadener--the Silentenna--at a Noise Reduction Conference. A top-rank scientist, John Wyvern, who is also attending the conference, mysteriously vanishes the day of the sonic attack.

Attempts on the lives of both Tom and Wyvern's pretty daughter intensify the young inventor's determination to solve the mystery. A clue to John Wyvern's whereabouts takes Tom to the sun-scorched Australian Outback, where he uses his latest invention-- robot bloodhound--to track down the missing scientist, but a deadly bush fire wipes out the trail.

Meanwhile, other cities in the United States have suffered terrifying eruptions of sound. The President receives an unsigned ultimatum, threatening an all-out sonic blitz unless the blackmailer's price of ten million dollars is paid.

Tom's Silentenna offers the only hope of defense--but to perfect it he needs a special liquid-crystal device which only the missing scientist can supply. The young inventor's race against time to thwart the unknown sonic enemy will keep every reader's pulse pounding with excitement and suspense.