"Trapezium, a quadrilateral with no two sides that are parallel."
Pitt rose from the table and moved until he was almost standing inside the three-dimensional chart of the ocean. "A bit unusual for the acoustic sources to all stem from islands." He turned and stared at Yaeger. "Are you sure of your data? There is no mistake, your electronic gear processed the tracking information from the hydrophone system correctly?"
Yaeger looked as though Pitt had stabbed him in the chest. "Our statistical analysis takes into account the acoustic network receptions and the alternative ray paths due to ocean variations."
"I stand humbled." Pitt bowed, making a gesture of apology. Then he asked, "Are the islands inhabited?"
Yaeger handed Pitt a small folder. "We've gleaned the usual encyclopedia of data on the islands.
Geology, fauna, inhabitants. Gladiator Island is privately owned. The other three are leased from foreign governments for mineral exploration. These have to be considered forbidden zones."
" How can sound be propagated such great distances underwater?" inquired Giordino.
"High-frequency sound is rapidly absorbed by salts in seawater, but low-frequency acoustic waves ignore the molecular structure of the salts, and their signals have been detected at ranges reaching thousands of kilometers. The next part of the scenario gets hazy. Somehow, in a manner we've yet to understand, the high-intensity, low-frequency rays, radiating from the various sources, surface and focus in what is known as àconvergence zone.' It's a phenomenon the scientists call `caustics.'"
"Like in caustic soda?" asked Giordino.
"No, like an envelope formed when the sound rays meet and converge."
Sandecker held up a pair of reading spectacles to the light, checking for smudges. "And if we were all sitting on the deck of a ship that was in the middle of a convergence zone?"
"If struck by only one sound source," explained Yaeger, "we'd hear a soft hum and maybe suffer from nothing more than a mild headache. But if four waves converged in the same region at the same time, multiplying the intensity, the structure of the ship would ring or vibrate and the sonic energy would cause enough internal organ damage to kill all of us within a matter of minutes."
"Judging from the scattered sites of the disasters," said Giordino grimly, "this thing can run amok and strike anywhere in the sea."
"Or along shorelines," Pitt added.
"We're working on predicting where the ray channels converge," Yaeger said, "but it's difficult to come up with a set formula. For the moment, the best we can do is chart tides, currents, sea depths and water temperatures. They all can significantly alter the path of the sound rays."
"Since we have a vague notion of what we're dealing with," said Sandecker, "we can lay out a plan to pull the plug."
"The question is," Pitt commented, "except for the mineral exploration companies, what do the islands have in common?"
Giordino stared at his cigar. "Clandestine nuclear or conventional weapons testing?"
"None of the above," Yaeger replied.
"Then what?" demanded Sandecker.
"Diamonds."
Sandecker stared at Yaeger queerly. "Diamonds, you say?"
"Yes, sir." Yaeger checked his file. "The operations on all tour islands are either owned or run by Dorsett Consolidated Mining Limited of Sydney, Australia. Second only to De Beers as the world's largest diamond producer."
Pitt felt as if someone had walked up and suddenly punched him in the stomach. "Arthur Dorsett," he said quietly, "the chairman of Dorsett Consolidated Mining, happens to be the father of the two women A1 and I rescued in the Antarctic."
"Of course," said Gunn, suddenly seeing the light. "Deirdre Dorsett." Then a quizzical look came into his eyes. "But the other lady, Maeve Fletcher?"
"Deirdre's sister, who took an ancestral grandmother's name," explained Pitt.
Only Giordino saw the humor. "They went to an awful lot of trouble to meet us."
Sandecker shot him a withering look and turned to Pitt. "This strikes me as more than a mere coincidence."
Giordino came right back. "I can't help wondering what one of the world's richest diamond merchants will have to say when he learns his diggings came within a hair of killing off his darling daughters."
"We may have a blessing in disguise," said Gunn. "If Dorsett's mining operations are somehow responsible for an acoustic death plague, Dirk and A1 have the credentials to walk up to his front door and ask questions. The man has every reason to act the role of a grateful father."