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.

A more detailed summary of this book is in preparation! Stay tunedÖ

The Silentenna is Tom's attempt to build a machine that can cancel out sound. The idea behind it is simple: the machine detects sounds, analyzes their wave pattern and then beams out a sound wave that is exactly out of phase with the wave it detected. These two waves would cancel themselves out, producing silence.

The reason Tom was developing a Silentenna was to solve the sonic boom problem. As is generally known, when a plane exceeds the speed of sound it creates a sonic shockwave that trails behind the plane. This shockwave is very dangerous: not only is it loud and annoying, it also has the ability to shatter windows, ruin crops, and in general cause widespread damage. This is one of the reasons why supersonic airliners do not sail the skies as futurists once predicted: no one wants an airplane that pulverizes the country it is flying over, so supersonic flight has largely been relegated to oceanic crossings. If someone could develop a way to cancel out or remove the shockwave the last hurdle to supersonic flight would be solved -- and that is exactly what Tom Swift hoped to do.

This is a well-established fact; airplanes use this method to reduce engine noise, and I have heard that some construction sites have implemented this sort of system to keep noise down to a manageable level. The problem, however, is that this method can't get the complete silence Tom was able to achieveÖ

Tom (who seems to be in a playful mood in this book!) plays the same trick later on a loudmouth know-it-all science-fiction writer who later tours his plant as part of a group of reporters. The problem, however, is that this scene isn't possible: while a Silentenna can reduce sound, it can't completely eliminate a series of sounds as complicated as a voice. Sound waves travel at a finite speed, and even at electron speeds it isn't possible to analyze a series of sounds like that quick enough and generate a countersound in time to create complete silence. There's more to it than that; but to sum it all up: it can't be done.

Of course, Tom's goal was not to create a way to silence the loudmouths of the world (although this does seem like a noble goal! Perhaps one of these should be instituted in the halls of Congress and used now and then at appropriate moments.) Tom wanted to cancel out sonic booms: was his invention a success doing that?

Actually, no, it was not. In Chapter II Tom Swift had his Mark II Silentenna installed on a plane (although he designed it for mounting under the wings of the Sky Queen). Tom held a public news conference to watch the testing, and in front of a crowd of reporters and officials Bud flew the plane, broke the sound barrier -- and created a sonic boom. Tom was heartbroken: his device helped muffle the sonic shockwave, but it didn't cancel it out.

Tom was confident, however, that he had the right principle. The Mark II worked a little differently than the Mark I:

Tom did not give up. Working closely with his Dad, he isolated the problem (a faulty crystal) and produced a new prototype. Instead of retesting its effectiveness in sonic booms, though, he instead used it to battle the sonic invadersÖ

Tom wasn't kidding. Tom stumbled upon the brainwashers when they kidnapped John Wyvern -- a scientist whose knowledge Tom desperately needed to defeat the blackmailers. Here is what Wyvern was like before the kidnapping:

When Tom finally tracked down Wyvern again he was in sad shape:

Earlier in the book when Tom found him in the Australian outback he was in even worse shape: he couldn't talk, he was completely out of his mind and he acted like an animal. The techniques the sonic brainwashers used were very effective: they had reduced Wyvern to little more than a vegetable. At the end of the book Tom and Bud themselves got a taste of the brainwashing treatment. It was crude but effective: simply blast very loud, raw sound at someone long enough and they will go insane. Would that really work? I don't know, but I sure don't want to find out! I suspect it wouldÖ

Speculations abounded. Soon San Francisco was hit with a sonic attack, and then Atlanta. The country was thrown into turmoil and fear; what was behind these attacks? Tom soon found out: he was summoned to the Pentagon and found out that:

So Tom's mission became clear: could he use his Silentenna to defend against the sonic attack? Tom decided to try; he was his country's only hope. At first Tom pinned his hopes on finding John Wyvern, for Wyvern was the only man who could build the crystals Tom needed for his Silentenna. When Wyvern was at last located and found to be a mental vegetable, though, that hope was dashed to pieces. Tom, for all intents and purposes, had failed!

This is unheard-of in the Tom Swift series: normally Tom would stay up late a few nights, eat some of Chow's sandwiches and (with a few mishaps and after being knocked out a few times) come up with the answer. After 26 volumes, however, Tom's luck had finally run dry: his invention failed and Wyvern -- the world expert that Tom needed -- had been brainwashed into insanity.

As Tom Sr. explained it, the activator was a simple matter:

Tom was thrilled. He changed his Silentenna to work with the new crystals and then tested them out; they worked perfectly. Armed with the new device, the President turned down the blackmailers. They retaliated by attacking New York City at the height of rush hour traffic. Tom's device saved the day: it reduced the sound to a bearable level, and he traced the sound to its source -- little flying devices he called screaming meemies.

Tom didn't know about the meemies until after he had silenced the attack on New York. Hank Sterling was the first to spot one:

If you ask me, the screaming meemies are far more amazing than they let on. An airplane the size of a grapefruit that can stay airborne for a day is a tremendous accomplishment -- it's simply not possible with today's technology. I imagine the Air Force would give a lot to have one of these: not only could they stay airborne but they had radar guidance systems, were remote controlled, and autonomous. And to think they could generate a sound loud enough to destroy a whole city! Clearly, these were some of the most brilliant enemies Tom ever faced. Perhaps such a feat will be visible a few hundred years from now, but not todayÖ

A much more realistic device is the Screaming Suzie in the Rick Brant book THE WHISPERING BOX MYSTERY. In that book, a group of criminals had built a device (a 'whispering box') that generated a certain frequency of ultrasonic sounds which knocked people out. The gang at Spindrift was given the assignment of creating a defense against that sort of weapon, and so they created the Screaming Suzie. Suzie worked along the same principles of the Silentenna: it detected a sound, analyzed it, and generated a countersound that canceled it out. The reason the device was called Screaming Suzie was because the cancellation wasn't perfect: while it did render the 'whispering box' harmless, it didn't completely eliminate the sound: it simply decreased it into an earsplitting wail.

Here's what the book has to say about the electronic mutt:

Tom doesn't claim to be the inventor of that kind of machine. Gull (filled with love for Tom, I am sure) pointed out that "Gray Walter's machines in England and 'the Beast' at the John Hopkins Applied Physics Lab are far more advanced and instructive." Tom, however, simply said that "ÖI hope Fido may offer some new angles on memory and learning" -- and, perhaps, he did.