y
from these silt beds."

Tom sobered. "You have a point there. I'd better have an audio screen
set up around this whole area. That'll act as a burglar alarm--and help
discourage the fish, too."

Twenty minutes later the boys were winging back to the mainland. When
Tom reached his office, he called in Gib Brownell, an Enterprises
engineer.

"Got a job for me, skipper?"

Tom handed him a hastily scribbled diagram of the audio-screen setup.
"One of those hurry-up deals, Gib," he said with an apologetic grin. Tom
explained his plan. "We'll use transmitter buoys, monitored by an alarm
system at base headquarters on Fearing."

Brownell studied the diagram and nodded. "Right. We can have it set up
in twenty-four hours."

As Brownell left the office, the telephone jangled. Tom reached for it.

"Admiral Walter calling." His voice was tense. "Important news, Tom. One
of our subs has picked up a clue that someone has been operating in the
missile search area."

"What sort of clue, sir?" Tom asked.

"A compressed-air caisson for underwater work. It had been driven into
the silt and then abandoned." Admiral Walter added that photographs and
a section of the caisson were being flown to the Naval Research
Laboratory for careful study. "I'll have a full report transmitted to
you by video as soon as it reaches my desk."

Tom thanked the admiral and hung up, feeling more uneasy than ever. The
report came through the following morning. Tom absorbed the contents,
then gave a low whistle.

"Trouble?" asked Bud, who had just dropped into the office with some
flight-test data on a new Swift superjet.

"Our old enemies again." Tom shoved the papers across his desk.

The report stated that both the design and manufacturing techniques used
in making the caisson indicated that it was of Brungarian origin. A
spectrographic analysis of the steels confirmed the theory. Their
metallurgical content agreed with known Brungarian steel formulas.

"The sneaky rats!" Bud cried out. "Well, at least we know now who
sabotaged our missile recovery."

As Tom paced about the office, Bud added, "What do you suppose they were
using the caisson for?"

"Probably as a base for some heavy, rotating search equipment," the
young inventor surmised.

"But why ditch it?"

Tom shrugged. "An optimistic guess is that they spotted our Navy search
force and pulled out quickly, fearing a surprise attack."

"What's a pessimistic explanation?" Bud asked.