the boys discussed the situation.

"Tom, if this was deliberate," Mrs. Swift pointed out, "Enterprises may
be next on the enemy's list!"

Tom did his best to allay his mother's fears, but inwardly he himself
felt apprehensive. Any large-scale sabotage plot would be almost certain
to include Swift Enterprises, America's most daring and advanced
research center.

When his mother went upstairs to her room, Tom suggested to Bud that
they drive to the nearby State Police post. Here he confided his fears
to Captain Rock, an old friend of the Swifts.

"You have some request in mind?" Captain Rock inquired.

"How about making a search for any signs of suspicious digging or
underground activity in the vicinity of Shopton?" Tom said. "There would
have to be an excavation of some sort in order to set off an underground
blast."

Captain Rock mulled over Tom's suggestion. "Sounds like a big job, but
I'm afraid you're right, Tom. We can't risk a similar disaster here."

"We'd better move fast, too," Bud put in. "Those two quakes so far came
only a day apart!"

Rock picked up the telephone and barked out orders. Within half an hour,
several carloads of troopers were covering the outlying roads that
converged on Shopton. Firemen and Chief Slater's town police force were
also pressed into action. They would search every cellar in town for
signs of recent digging.

Bud rode in one police car and Tom in another as a house-to-house search
was conducted along the highway that ran past Enterprises.

At one weather-beaten house, where Bud stopped with a state trooper, an
old man came to the door.

"What you fellers prowlin' around for?" he asked.

"Bomb emergency," the trooper said laconically. "We have orders to
search every house cellar for underground openings."

Grumbling, the old man let them enter. He followed them down a rickety
stairway. A moment later Bud stumbled and gave a yell. The trooper swung
around just in time to see Bud drop from view!

CHAPTER V

SECRET CACHE

As the trooper's flashlight stabbed through the cellar gloom at the spot
where Bud had disappeared, there came a loud splash! The light showed a
round hole in the floor, rimmed by a low circle of brickwork.

"What's that hole?" the trooper snapped at the owner.

"What does it look like?" the elderly man snapped back. "It's an old
well."

"A _well!_" the trooper exclaimed as he rushed to the spot. "And not
even covered? What're you tryi