goes wrong!"

"Bring food--that's my motto," Chow retorted, "like any good cook."

Minutes later, after a parting handshake from his father and a worried
kiss from Sandy, Tom sent the sleek jet racing down the runway for
take-off. Soon they were air-borne and heading westward. Chow served a
tasty meal en route.

It was still daylight when the jet landed vertically in the Colorado
canyon. The government crew manning the installation, and the Swift
technician who had relieved Art Wiltessa as trouble shooter on the
setup, greeted them eagerly.

"Looks as if we're in for a real test, Tom," said Mike Burrows, the
engineer in charge.

"Let's hope we pass!" said Tom, holding up crossed fingers.

He checked every detail of the Quakelizor, power plant, and the
communications gear. He opened an inspection panel in each of the
dual-control spheres and tuned the kinetic-hydraulic units so as to
step up the working pressure of the four powerful drivers.

"Well, all we can do now is wait," the young inventor muttered, wiping
his arm across his forehead.

Tom passed the night in a fitful sleep, half expecting to be wakened at
any moment by the stand-by crew on watch. No alarm occurred, however.

Dawn broke, and Chow delighted all hands with a hearty breakfast of
bacon, eggs, and corn fritters. More hours of waiting dragged by.

"What time do you think the attack will occur?" Bud asked.

Tom shrugged. "The 'twenty-four-hour' business may have been
approximate. But I'd say from two o'clock on is the danger period."

The young inventor checked frequently with Washington and the other
crews stationed around the country. Suddenly the radiotelephone operator
gave a yell.

"Your father is on the line, skipper!"

The scientist was calling from the receiver-computer headquarters at
Enterprises. "Exman has reported a quake pulse will be sent in seven
minutes--at 21.36 G.M.T."

"I'm ready, Dad," Tom said, then asked for various technical details
before hanging up.

He passed the word to the crew and glanced at his watch. A hasty,
last-moment inspection was carried out, every man checking certain
details of the setup.

Soon the pulsemakers began ticking inside the dual-control spheres as
they picked up the frequency signal by radio. Tom studied the gauge
dials.

Tension mounted rapidly among the waiting group. The same thought was
throbbing through every mind:

_Was the nation on the brink of a terrible disaster? Or would