Fourteen hours later the Esperance made ready to sail from Thrawn Island. Her purpose was to carry the plastic objects to Manila, where they would be turned over to specialized laboratories to be studied. Five such objects had been found before: one in the Thrawn Island lagoon, while the satellite-tracking station was under construction, and four attached to exotic fish brought to market by the commercial fishing boat La Rubia. Now there were eight more, of four different kinds. To the laboratories would go Terry's observation that one kind of these objects absorbed sound at audible frequencies and retransmitted it at much higher ones, but only under water. All this was very interesting and very puzzling.

But a serious disturbance had arisen at the tracking station.

Dr. Morton came to the Esperance before her departure. He had a problem. He'd predicted to the minute, and almost to the mile, the landing of the bolide of the night before. That was the first accurate prediction of the kind in history. But his forecast stood alone in its precision. Nobody else had even come near being right. Now he was being insistently queried by astronomers the world over. They wanted to know how he'd done it. In particular, they wanted to know how he'd figured that the bolide would lose just so many feet per second velocity, neither more nor less, in a three-quarter orbit around the world. Nobody else had such a figure in his equation for the landing spot. Dr. Morton had. His prediction had been exact. Where did he get that necessary but inexplicable figure?

He beckoned Davis and Terry to go below with him, in the Esperance's after cabin. Terry hesitated.

"You may as well hear my troubles," said Morton vexedly. "You're largely responsible for them."

Terry followed uneasily. He didn't see how Dr. Morton could hold them responsible. He had guarded his own guesses about the Esperance's discoveries against even the slightest expression. He couldn't let himself believe in their correctness, but he was appalled at the inadequacy of all other explanations of past events.

"In sixteen months," said Morton annoyedly, down below, "we've spotted six bolides coming in to land in the Luzon Deep. That's out of all reason! Of course, it could be a mathematical series of wildly unlikely coincidences, such as probability says may happen sometimes. Up to last night that seemed to be a possible explanation."

Davis nodded. His expression was odd.

"But now," said Morton somehow indignantly, "that's ruled out! It's ruled out by last night's bolide, and yesterday's fishing experiment, and that business of the shining sea, plus those damned plastic gadgets and deep sea fish thriving in shallow water! There's no reasonable explanation for such things, and they're not mere coincidences!"

"I'm afraid," admitted Davis, "that they're not."

"The obvious explanation," said Morton doggedly, "I refuse to name or consider. But nevertheless the question is not whether a theory or an explanation is unlikely or not. The question is whether it's true!"

Davis nodded. Terry had to agree. But the way people are trained in modern times puts a great emphasis on reason, often at the expense of fact. Terry felt the customary civilized reluctance to accept a statistically improbable idea.

"I'm on a spot," fumed Morton. "I calculated that the damned bolide would slow after it went into orbit around the earth. I calculated that it would slow exactly so much. Do you want to know how I figured how much it should slow down? I'll tell you! I calculated exactly how much it would have to slow to be able to fall into the Luzon Deep! It did slow. It did fall there. But how am I going to explain that to Washington?"

Terry suddenly felt a warm sympathy for Morton. It is bad enough to dispute with oneself when something incredible happens. But Dr. Morton had gone out on a limb. He'd been caught psychologically naked telling the truth, and now he was asked to explain it. And he couldn't.

"This thing has got to come to a head!" he said angrily. "Sooner or later they'll find out that I don't calculate where it'll land by its behavior in space but by its landing spot! Davis, you've talked about stirring something up. For Heaven's sake, do it! You may save my reputation! And you...."

"I'll try to think of something," said Davis reservedly.

"I've got to have proof that my suspicions are right or wrong before I'm ruined. I know what you're planning to do. Do it! Is there anything that can be done here to help?"

Davis spread out his hands helplessly. But Terry said, "Yes. Send a boat every so often to listen at the gap in the reef. Put an oar overboard and put your ear to the handle. You should hear the underwater hum, if it's still there. It was there this morning."

Morton looked at him suspiciously.

"Why check on it? Should it change?"

"Perhaps," said Terry. "We've speared most of the deep-sea fish in the lagoon. Maybe we've interfered with ... the reports from the plastic objects, telling what was happening up here. There may be a reaction. If so, most likely the humming will stop, and after a longer or shorter time begin again. And then, if my guess is right, there'll be more deep-sea creatures in the lagoon."

"Ha," said Morton. "I think you and I have the same kind of delusions! All right. I'll see that that's done. You two do the rest."

He went abovedecks. When Terry got on deck, Dr. Morton's angular figure was already marching along the wharf to the shore.

There was no ceremony of departure. The Esperance cast off and her engine started. She moved toward the lagoon entrance under power only, but her sails were hoisted as she floated on, and Jug Bell was trimming the jib when she cleared the opening to the sea.

The humming in the water was still audible to the submarine ear, close to the land. It occurred to Terry to take a bearing on the source of the sound, noting both the compass direction and the vertical angle from the reef. If his vertical-angle reading was accurate, a line from the reef to the source of the sound would touch the bottom at twenty-seven thousand feet down, between four and five miles away.

The Esperance sailed on. The humming duly faded away. Terry left the recorder picking up undersea sounds, without recording them. It relayed the underwater sounds to the people on deck. It was in Terry's mind to keep at least half an ear cocked to it, in case the mooing sounds, heard and recorded elsewhere, should come again.

They did not. The Esperance went methodically on her way, headed south by east, under sail. A slowly swaying horizon of unbroken sea was all about. There was nothing in the least unusual or mysterious to be seen anywhere.

Presently, Terry found himself in conversation with Deirdre, and the world seemed so blatantly normal that their talk dodged all unusual trends. They talked about their childhoods, about things they had done and places they had seen.

At about four in the afternoon Nick bellowed, "Thar she blows!" in a fine attempt at proper whaling ship style, and all the Esperance's company joined to watch a spouting far ahead. The yacht changed course a little, and presently reached a pod of sperm whales at the surface. The huge dark bodies moved leisurely through the water. Jud displayed great erudition on the subject and explained in detail how their spouting proved them to be sperm whales. Deirdre pointed out a baby whale close beside a larger one.

They sailed on, leaving the whales behind. The crew-cuts, inevitably, argued about them. They canvassed all the information and misinformation they possessed and came up with a heated discussion about whales, how they can swim down to the enormous depths without suffering from the bends on rising again. Then the conversation turned to the food they eat. Whalers, in the old days, had found snouts of squids and undigested sections of squids' tentacles in the stomachs of harpooned sperm whales. There were reports of sections of tentacles four feet thick, implying a startling total size, all of which proved that the whales had been at the bottom of the ocean, where such gigantic squids can be found. These were the reports of reliable whaling skippers. Certainly the scars made by the tentacular arms of huge squids, indicating battle, have been found on the skin of sperm whales, and there have been reports of battles on the surface between whales and squids of sizes most naturalists would be unwilling to certify. In such cases it was assumed that the squids had been attacked at the bottom of the sea and had followed the whale to the surface when it came up in need of air. Certainly only an enormous squid would be able to sustain a battle with a whale.

Terry listened to the discussion. Everybody had his own opinion.

"You'd never settle the argument, unless you could put a camera and a flash gun on a whale and get an instrument-report from it."

Which was not a new idea, of course. But it was curious that the thought of sending self-reporting instruments down to the bottom of the sea had been suggested by his own suspicion that similar instruments had been sent up from below. Sounding lines had been lowered with thermometers and nets and sampling machines. Core-takers had been dropped to get samplings of abyssal mud. But tethered instrumentation is never more than so useful.

Deirdre said something. Terry realized that she'd repeated it. He'd become absorbed in the possibilities of instrument-reporting from the surface to the depths and back again.

"You're not listening," protested Deirdre. "I'm talking about the bathyscaphe that ought to be in Manila any day now."

"I'm trying to picture myself going down in a bathyscaphe," said Terry hastily. "I don't think I'd like it."

A bathyscaphe is a metal sphere with walls and windows of enormous thickness, hung from a metal balloon filled with gasoline for flotation. It is lowered to appalling depths with the help of heavy ballast, and is equipped with electric motors for independent motion. It carries powerful electric reflectors which allow as much as thirty or forty feet of visibility. It rises to the surface again when its ballast is dumped. There are only three such undersea exploring devices in the whole world.

"I'm not at all sure you wouldn't like it," said Deirdre.

Terry scowled at his own thoughts. There are opinions a man holds firmly without ever being aware of them, unless they are challenged, and if that happens, he is deeply suspicious of the challenge because it suggests that his opinion needs to be re-examined. Terry had been gathering scraps of information here, and unquestionable items there, resisting a conclusion all the while.

It seemed fantastic to think that the plastic objects carried by deep-sea fish out of their natural environment were actually man-made instruments—telemetering apparatus closely comparable to the devices used to transmit information from outer space. It was wildly imaginative to suppose that they transmitted information from the water surface to the depths of the ocean; that fish had been driven up from the abyss in order to report what went on at the surface. Report to whom? It was the most fantastic of fantasies to think that there was curiosity, in the Luzon Deep, about the manners and customs of the inhabitants of the surface waters and of those areas not covered by the sea.

But Terry stopped short. There were limits to the ideas he would allow his brain to think about.

Deirdre walked away, and he assured himself he never thought of anything so ridiculous as the conclusions he had just reached. Presently, dinner was served, and Terry painstakingly acted like a perfectly rational person. After dinner Davis, as usual, settled himself down to enjoy a program of symphonic music from San Francisco, many thousands of miles away. And Deirdre vanished from sight again.

Later on Terry found himself alone on the Esperance's deck, except for Nick at the wheel—a mere dark figure seen only by the light of the binnacle lamp. There was a diffused, faint glow coming from the after-cabin hatch. Up forward, one of the crew-cuts plucked a guitar, and Terry could imagine Doug dourly trying to read poetry despite the noise. The sails were black against the sky. The deck was darker than the sea.

Terry's guesses haunted him. He assured himself that he did not entertain them even for an instant. They were absurd! A part of his mind argued speciously that if they were absurd there was no reason not to test them. If he was afraid to try, it would imply that at least part of him believed them.

He picked up one of the plastic objects, and moved the recorder close to the lee rail. It still transmitted faithfully, at minimum volume, the washing of the waves as heard from beneath, and occasional small sounds from living creatures, generally far away in the sea. Heeled over as the Esperance was, his hand could reach down into the rushing waters overside.

He came to a resolution. He felt foolish, but by now he was determined to try an experiment. Tiny light-blue sparks flashed where the water raced past the yacht's planking. When he dipped his hand, water piled up against his wrist and a streak of brightness trailed away behind.

He tapped the plastic object against the hull. One tap, two taps, three taps, four taps. Then five, six, seven, eight. He went back to one. One tap, two, and three and four. Five and six and seven and eight.

The recorder gave out the tappings the underwater microphone had picked up. It seemed to Terry that the loudspeaker struggled to emit the shrillest imaginable sounds in strict synchrony with the tappings.

Then Deirdre's voice came quietly, very near.

"I don't think," she said evenly, "that that's a fair thing to do."

He'd been bent over the rail in an awkward position. He straightened up, guiltily.

"I know it's nonsense, but I was ... ashamed to admit ..."

"To admit," Deirdre concluded for him, "that by tapping numbers with a plastic spy-device, you hoped to say to whom it might concern that we've found a communicator, and we know what it is, and we're trying to get in touch with the intelligent creatures who made it."

To hear his own self-denied guesses spoken aloud was appalling. Terry instantly disbelieved them entirely.

"It's ridiculous, of course," he protested. "It's childish...."

"But it could be true," said Deirdre. "And, if true, it could be dangerous. Suppose whatever put those plastic gadgets on the fish doesn't want to be communicated with? Suppose it feels that it should defend the secret of its existence by killing those who suspect it? I wasn't spying on you," she added. "I heard the tappings down below."

Then she was gone. He saw the interruption in the light from the after-cabin hatch as she went below.

He was suddenly filled with horror at the idea that if his guesses did prove to be right, he might have endangered Deirdre. And then he ceased to feel foolish. He felt like a criminal instead.

For a long, long time he listened with desperate intensity to the recorder, lest he hear some reply to his signals.

But no answer came. The sounds from undersea remained utterly commonplace.

When morning arrived he was in a state of desperate gloom. At breakfast Deirdre acted as if she considered the incident closed. And, such being the nature of men, Terry felt worse than before.

He was not wholly at ease again, even when that afternoon the Esperance sailed in past Cavite and Corregidor and into Manila Bay. A new ship was at anchor in the harbor. It was a stubby, stocky ship which Davis regarded with interest.

"That's the Pelorus," he told Terry as the yacht passed within a mile, on the way to her former anchorage. "She's the hydrographic ship with the bathyscaphe on board. We'll visit her. I'll get Nick to call her on short-wave."

He went forward, where Nick was making ready to drop the anchor. Davis took over the chore, and Nick went below.

"Are you going ashore?" asked Deirdre.

Terry shrugged. "I've no reason to."

She looked relieved. "Then you'll stay with the Esperance until—things are settled one way or another? I mean, you're really enlisted?"

"Until there are no more ways left for me to blunder," said Terry distastefully. "I'm about through the list, though."

"Not at all!" protested Deirdre. "Tapping numbers was really a very good idea. I was horrible! I scolded because you'd kept it a secret from me. I'd have been proud if I'd thought of it first!"

Nick came back and spoke to Davis. Davis came aft.

"The Pelorus will send a boat as soon as we've anchored," he told them. "They've heard something and want to see the plastic objects."

"I'd like the long end of a bet that they don't believe in them, or us," Terry said abruptly. "They're established authorities on the ocean bottom. They know a lot. They probably know so much they can't really believe there's anything more to know than what they're busy finding out now."

Davis shook his head. He was confident. The Esperance anchored, almost exactly where she'd been when Terry first came on board. Within half an hour a boat arrived from the Pelorus. Terry repeated his refusal to go along. Deirdre went along with her father.

They came back a little over an hour later. At first Davis was almost speechless with fury. Then he told Terry, choking on his rage, "According to them, the plastic objects are a hoax. The hum is a school of fish. We aren't trained observers. At Thrawn Island they're astronomers and they simply don't know anything about biology. And we should realize that it's starkly impossible for intelligence to develop where the oxygen supply is limited. It's unthinkable that abyssal fish should have their swim bladders punctured so they won't explode from release of pressure when they come to the surface. Those in the lagoon aren't abyssal fish, just unfamiliar species!"

"Well?" Terry asked.

"Oh, they're going to make a bathyscaphe dive!" said Davis as angrily as before. "As a matter of courtesy to somebody—not us. They'll make it where we found fish packed in a circle. That happens to be the deepest part of the Luzon Deep, in any case. They don't object to our sending our dredge down first. They will be politely interested if it comes back up."

"I," announced Deirdre, "I am so mad I could spit!"

"There's no use in our staying here," said Davis, seething. "Our dredge should be ready. We'll go up to Barca and tow it to the point we want to send it down."

He ordered Nick to get ready to lift anchor.

"One question," Terry said finally. "Did you mention the bolides?"

"No!" snapped Davis. "Would I want them to think I was crazy?"

He stamped away.

The Esperance put to sea again. She sailed north along the coast. At dinner everybody was quiet. It was the only meal, since Terry's joining, that had not been enlivened by an elaborate argument on some subject or other. Davis was still in an abominable mood. He knew it, and held himself to silence.

Later, Terry and Deirdre talked together. They refrained tacitly from speaking of marine biology or any reasons for tapping plastic objects against the Esperance's hull. They discussed only trivia, but somehow Terry found any subject absorbing, when he was with Deirdre.

After a while she went below, and he stayed abovedecks, smoking. The moon had not yet risen when he turned in.

They sailed into the small harbor of Barca at ten in the morning. By twelve, local boatmen had towed out an ungainly object some thirty-two feet long. They tethered it to bitts at the Esperance's stern. By one o'clock they had loaded on her deck a large, folded sack of sailcloth and half a dozen specially-cast concrete blocks with eyed iron rods cemented in them. At half-past one Deirdre, who had gone ashore in one of the yacht's own boats, came back with innumerable supplies she'd bought. At two o'clock the Esperance went out to sea again.

The towed object was a construction around a central wooden spar with an iron tube at its top end and half a dozen lesser spars linked loosely to its bottom. A mass of fishnet was fastened to the smaller spars and heavy ropes were holding the spars and the net in place during its tow. There was a hook for attaching the main spar to the concrete sinkers.

"It opens like an umbrella," explained Deirdre. "We'll hoist it upright barely out of the water, and fasten on the weights. The canvas bag fits on that iron pipe. When you let it go, it sinks like an umbrella that's tightly closed, but when it touches bottom the weights spread it out and an explosive charge automatically goes off in that iron tube. It's special explosive. The gas it makes inflates the canvas bag, which can't burn underwater, and that floats the whole thing back up with the ribs of the umbrella stretched out and spreading the net between them. It should catch anything it encounters as it rises. As the pressure lowers, the excess gas can escape through a relief-valve. This dredge is experimental. If it works, it can be modified to do lots of things."

"Such as poking at things we don't believe in," said Terry drily. "That explosion ought to stir up anything in its neighborhood. It'll be much more disturbing and audible than a few light taps against the Esperance's hull!"

Deirdre grinned ruefully and did not answer.

The bulky tow slowed the yacht. She did not reach the position of the fish-filled circle until after nightfall, and it was necessary to have plenty of light by which to locate the inflated bag when it came to the surface, so nothing could be tried until the following morning. A short while before daybreak, lights appeared at the horizon. Red and green sidelights, and white central lights. It was a steamer. It came closer and closer. Presently, it turned and headed upwind and went dead slow, barely keeping steerage. It was the Pelorus.

Dawn arrived in a golden radiance which thrust aside the night. The Pelorus shone brightly in the first rays of the sun. A large object was hoisted out of her hold. Its shape was that of a gravid goldfish, with a smaller sphere hanging beneath it. It went overside, slowly, and there it floated, rolling wildly on the waves. For a very long time nothing seemed to happen. Then the water-level of the float sank a little. It was being filled with gasoline, which is lighter than water and practically incompressible.

On the Esperance, the tow had been pulled alongside and the yacht's powerful winch hauled it upright. The yacht heeled over from the weight. The crew-cuts fastened the canvas sack in place, and Davis loaded the explosive charge into the iron tube. The crew-cuts cleared the nets. This preliminary operation seemed promising, and it was quite likely that the dredge would operate as it was designed to do.

The Pelorus whistled impatiently. Nick abandoned his job and went below to the short-wave set. He returned shortly after.

"The Pelorus says she'll be ready to send the bathyscaphe down for a test dive in two hours," he reported. "She says she will object if our gadget is floating free at the time, on the chance that it might interfere with the bathyscaphe. She asks if you can send our dredge down right away and get it over with."

"Tell them yes," said Davis. "In five minutes."

He compressed his lips. The Esperance's device, though clumsy, was fundamentally simple. Five minutes later the top of the central spar was level with the water. "Cut away," said Davis.

Doug slashed the single rope holding the dredge. It sank immediately.

The recorder gave off the sound of waves. Occasionally, very occasionally, a chirping or a grunt could be heard. Twenty minutes. Thirty.

There was a "crump!" from the loudspeaker which reported underwater events. The sound seemed to come from very far below. Even a small amount of explosive makes a very considerable concussion when it goes off so far down, and the shock travels in all directions instead of merely upward. The recorder picked up that concussion as a deep-bass sound.

The sun shone. The wind increased. Waves marched in serried ranks from here to there.

A long, long time later the inflated canvas bag came up and was floating on top of the waves. The Pelorus whistled. Nick went below. A few minutes later he came up again to report.

"The Pelorus says not to cast our dredge adrift. They're sending the bathyscaphe down unmanned, to test all apparatus before a manned dive. They don't want any debris in the sea."

"Tell them we send them a kiss," snapped Davis, "and they needn't worry!"

The Esperance approached the floating bag. Jug swung out on the lifting boom and hooked it. The winch hauled it out of the water. The concrete weights were gone. What the nets had captured was not pretty to see. A dead fish with foliated appendages had come up from far below, to judge by what its unpunctured swim bladder had done to it in uncontrolled expansion. Davis said curtly it was Linophrine arborifer, belonging two thousand fathoms below. An angry-looking creature, similarly dead, was Opisthoproctus grimaldi. It belonged deeper than the other. There were other specimens. A genostoma of a species the books didn't picture; a Myctophum; and various other creatures, mostly as grotesque as their scientific names. All were abyssal fish. They had died while rising from a pressure of several tons per square inch to surface-pressure only.

"It worked," said Davis curtly. "I almost wish it hadn't. Let it down into the water again. We'll jettison it when the Pelorus gives us permission."

Time passed. More time. Still more. The bathyscaphe was now in the water, practically awash. Only a small conning tower showed above the waves. Men swarmed around it.

There came a query from the Pelorus. The Esperance gave assurance that the deep-sea dredge had returned to the surface and would be kept there.

The bathyscaphe was allowed to sink.

The recorder on the yacht began to pick up deep-toned mooing sounds from the depths.

Presently, the mooing sounds ceased.

Two hours later, waves broke over an object completely awash on the ocean. The Pelorus steamed cautiously toward it. Boats went down from her sides and surrounded the float.

After a long time the Pelorus got alongside and men quickly fastened the huge buoy to the ship. Then the down-wind sea changed its appearance. A reek of gasoline reached the Esperance.

"Something happened," said Davis dourly. "They're dumping the gasoline—not even pumping it aboard. Let's get out of the stink."

The Esperance beat to windward. The Pelorus began to lift something large and ungainly out of the water. The Esperance went down-wind to take a look at it.

The yacht went past no more than fifty yards away, just as the bathyscaphe left the water and swung clear.

The bathyscaphe's conning-tower was gone. It had been torn away by brute force. The three-inch-thick steel globe.... Half of it was gone. The rest was crushed. The sphere, which had been designed to resist a crushing pressure of ten tons per square inch, had been ripped in half! It had been bitten through. Bitten!

There was no comment by anybody on the Esperance.

Half a mile from the oceanographic ship, Davis said in a peculiarly flat voice, "Cut away the dredge. We won't try to use it again."

Someone slashed the inflated canvas bag. It collapsed. Somebody cut away a rope. The free dredge sank, slowly. It would never come up again.

The Esperance changed course. She headed north by west. There was still no conversation at all. The yacht seemed to tiptoe away from the scene of the bathyscaphe's destruction.

A long time later, Deirdre said tentatively, "Have you been making guesses, Terry?"

"Guesses, yes," he admitted.

"Such as?"

"Your father denied that the dredge was designed to stir up whatever gathered the fish together and then carried them down to the bottom of the sea. I was right there with him in the denial, but that's what we intended, just the same. We said we didn't believe there was anything there, so it couldn't do any harm to poke it. We poked, all right! Our dredge, and then the bathyscaphe...."

"But what ..."

"And a bolide fell right there a couple of nights ago," said Terry irrelevantly. "I wonder what the entity on the ocean-bottom thought of the bolide. Hm." He paused. "I wonder, too, what the bolide thought of what it found down there. Is that too crazy for a sane man to think, Deirdre?"

She shook her head.

"Why is my father working on this business?" she asked. "And why are the boys helping, and why do radar stations tell us what they find out, and why did the Philippine Government ask the Pelorus to make a bathyscaphe dive at just that spot?"

Terry blinked at her.

"Too crazy for official notice, eh?" he said, "but too dangerous not to check up on! Is it absolutely certain that the bolides are bolides?"

"No."

"Thanks," said Terry. He pursed his lips as if to whistle. "I've been thinking of this thing as a puzzle. But it isn't. I'm very much afraid it's a threat!" He paused. "Y-y-es. I've just made a new guess. It adds everything together. I do hope it's wrong, Deirdre! I've got cold chills running up and down my spine!"