his caller added, "I
hear you're planning a square dance Tuesday night at the yacht club."

Suddenly Tom remembered. Lester Morris was a popular dance orchestra
leader in and around Shopton. He was also much in demand as a
square-dance caller and fiddler.

"That's right," Tom said with a chuckle. "News must travel fast. We just
phoned invitations to our friends."

Morris asked if musicians had been hired for the evening. When Tom said
No, his caller volunteered for the job, offering to provide a small
combo of country-style players. His asking price sounded like a bargain
rate, and Tom, knowing Morris's reputation, was only too glad to engage
him.

"Lucky break, his calling," the young inventor thought as he hung up.

Bud was delighted to hear of the arrangement when he came into the
laboratory a while later. The boys talked over their dance plans for a
few moments, then Bud asked:

"How's our underwater talkie system coming?"

Tom scratched his jaw thoughtfully. "A bit tricky but not too
difficult," he replied. "It's mostly a job of adapting the sonarphone
arrangement from our Fat Man suits--in miniature."

A tiny mike, Tom explained, would be installed on the inside of each
face mask, with its output feeding to a sonar transducer on the
exterior. The receiving transducers would feed from amplifiers to
earphones. The hookup would be powered by the solar battery in the
hydrolung power unit, by connecting wires through the breathing tube.

"That's neat, Tom," Bud said. "Need any help?"

"You can mold us a pair of new face masks--big enough to cover the
earphones," Tom suggested. He handed Bud a penciled sketch from the
workbench, adding, "Then drill the holes for the mikes and
earphones--the dimensions are there on the drawing. But watch it so
you don't crack the plastic."

[Illustration: _Chow was wild-eyed with panic!_]

While Bud complied, Tom began assembling the tiny electronic parts. In
two hours the gear was ready for testing.

Tom wiped his perspiring forehead and gave Bud a grin of satisfaction.
"Go get your swim trunks, fly boy. Let's give it a tryout in the tank."

"Swell idea! Be back in a jiff!"

After a quick change, the boys strapped on the new hydrolung equipment.
Before adjusting his face mask, Tom mentioned that he had inserted
scrambling circuits into the communicators to foil any enemy
eavesdroppers.

"If they do pick up anything, it'll sound like chop suey," Tom ended
with a chuc