There were also the special instruments designed to detect any accelerations which might occur if a significant gravitational pull, in addition to that of the earth, were to occur. All these instruments were connected to a small but powerful computer energized by the portable generator whose noise disturbed the otherwise quiet early afternoon. This computer would provide an instant analysis of the data. It not only recorded the strength of the signals but, using information from instruments spaced at a distance, it could also triangulate and determine the direction and distance to the source of the waves or gravitational acceleration.

All was now in readiness. Gantt felt a small chill despite the heat. In a little over an hour the seismic waves should broach the surface about two hundred miles away in eastern Arizona, registering on the seismometers but perhaps only marginally on the accelerometers even with Runyan's most extreme estimates. Eighty and a half minutes later the source of the waves would again approach the surface but a thousand miles to the west, over seven hundred miles off the Pacific coast. Since the incommensurate period of rotation of the earth made the surfacings appear to shift one hundred ninety miles every twenty-four hours, tomorrow at nearly the same time the waves should impinge on the surface very close to their present location.

Gantt turned his back on the encampment and looked out across the shallow hills. He had great difficulty accepting the picture proposed by Runyan, and yet he could not resist a morbid temptation to imagine what was proceeding if the hypothesis were correct. A small speeding object was now plunging down through the deepest basalt layers of the earth's crust. In fifteen minutes it would enter the molten core, picking up speed as it went. Sensing the change in gravitational pull as it passed the earth's centre, it would begin to slow as it shot back towards the surface, where it would peak with majestic slowness before crashing back into the dirt and rock.

Gantt shook his head and strode back to the main tent of the encampment. The interior of the tent was a little cooler because of the air conditioner installed to service the computer, but it was still stifling. Gantt became too engrossed to notice.

At five minutes before the appointed time, he focused his attention on the needles of the seismometers. They jiggled steadily but with nearly constant amplitude, tuned to the basic constant sounds of the earth. In a couple of minutes he saw the effect he was looking for. The swings of the needles on all three seismometers began to slowly grow in amplitude. Danielson's seismic waves were real enough all right. The question was what caused them. Even to Gantt's framed eye the signals on the three instruments looked identical. Only the computer could distinguish the minute differences due to the slightly different distances of the instruments from the source of the waves. Gantt turned to the computer, typing rapidly on the keyboard and then scrutinizing the screen in front of him as the printer to one side began to roll out the same data on a chain of paper sheets. The distance was about one hundred ninety miles, a little closer than their best guess, but within the expected errors. Gantt's gaze then swung to take in the readings from the accelerometers which might detect some variation in gravitational force. He thought he could make out the briefest fluctuation, but could not be sure. Again he keyed the computer and found his impression confirmed. There might be an effect, but it was only marginally above the noise level. A more sophisticated analysis that could only be done with time and a bigger computer might dig something out, but for now there was no firm conclusion to be reached. Still, he mused, an effect of the size Runyan predicted could not be ruled out. If the minute fluctuation were real, then something massive had just surfaced two hundred miles away, and in three quarters of an hour it would do so again on the far side of the earth.

Gantt stripped the printed computer output off the machine and examined it more carefully. He swore quietly as sweat dripped off his brow onto the paper, obscuring a few numbers. He stopped to wipe his forehead and neck and then returned his attention to the rows of numbers. The seismic waves stopped several miles below the surface. After a minute or so, the source of the waves began again, moving nearly vertically down into the earth. Gantt felt a nervous tightening across his abdomen. An ordinary seismic wave could be reflected, but it did not wait a minute while making up its mind. Such a delay might occur if the source of the waves moved up into light surface layers which were not conducive to the production of waves and then fell back again. Runyan's hole could do that. Deep in thought, Gantt sat for some minutes striving for an explanation in terms of the normal behaviour of the earth as he knew it. Nothing occurred to him, but he told himself that Runyan need not be right on that basis, perhaps it was just his own lack of imagination or lack of sufficient information. The mysterious interior of the earth had surprised him more than once and might be doing so again. Taking solace from that thought, he proceeded to a close study of the data acquired during the event.

Wednesday morning Pat Danielson clambered down from the rear seat of the jet-black F-16 which was rigged for tactical reconnaissance. She was aided by the pilot and a ground technician. Her legs were a little unsteady from the excitement of the Mach 2 flight from Washington — over two thousand miles to the Yuma Air Station in an hour and a half. She followed a young marine to a waiting helicopter and stood there while he went into a nearby utilitarian terminal building. He reemerged in a moment followed by Alex Runyan. Runyan was halfway across the tarmac when he looked up and saw her. The look of surprise and pleasure on his face was delicious to her.

'Pat!' He ran forward, grabbed her hand in both his and gave her a spontaneous peck on the cheek, oblivious to the watching servicemen. 'What a delight. I didn't expect to see you here.'

'After you pleaded with Bob Isaacs yesterday,' Danielson said gaily, 'we decided to coordinate the trips, save a helicopter ride.'

'That's great. When did you leave? It's a long way.' She laughed with obvious glee. 'Crossing three time zones helps, but so does that,' she pointed towards the fighter.

'We landed before we took off.'

'Holy cowl' Runyan exclaimed. 'Now I know who has the real clout. I thought I was Mr Big with the puddle jumper your boss arranged for me this morning. Well, let's get on with the adventurer

He helped her through the passenger hatch in the side of the helicopter, banded up her light bag, then his and finally swung himself up and in with a single easy motion.

'What did you think of Gantt's preliminary report?' Danielson shouted over the whine of the cranking engine, as they budded themselves in.

'Too soon to tell,' he shouted back, 'but I'm afraid there was nothing to prove I was wrong.'

After they took off, the flight noise made conversation difficult. Danielson watched the country flash by the open hatch, vividly aware of Runyan's long lean thigh next to hers.

Gantt was engrossed in making some changes in the computer analysis routines when he heard the chopping roar of the approaching helicopter. He approached the landing site and stood a hundred yards off as the machine circled once around the area and then settled slowly to the ground. As die rotor speed decreased and the whine of the turbojet ceased, he saw a man get out and then turn to help his companion. Gantt squinted into the sun and then finally waved a greeting as he recognized the approaching figures.

'Hello!' shouted Gantt. 'Alex! What a surprise. I didn't expect an extra guest at our little party here.'

He shook hands with Runyan and then with Danielson. He grabbed the young woman's hand with both of his and gave an extra shake. He suddenly wanted Danielson to feel welcome as a colleague, rather than a visiting government official.

'Do you have baggage to unload?' he inquired.

'Just a couple of bags,' replied Runyan. 'Lord, it's hot here! What's the temperature?'

'About a hundred and fifteen in the shade,' Gantt laughed. 'Cools off in the evenings, though. Not so bad then.'

Gantt looked back and saw the pilot unloading two small cases from the passenger compartment. He called to one of the young marines who had been recruited for the project to lend a hand and then ushered the pair into the mess tent.

'Can I get you something? Coffee? Iced tea? Lemonade? Lunch won't be ready for a while, but we might scare up a snack.'

Both declined anything to eat. Gantt got a cup of coffee for himself and showed the others where to help themselves to iced tea. They sat at a table under the outstretched flap of the tent, shielded from the sun but open to the fitful breeze.

'Well, Alex, I needn't ask what brings you here, but it is a pleasant surprise.'

Runyan wiped his brow with the back of his hand and scratched his hot beard.

'I've been living with the computer at the Jet Propulsion Laboratory, adapting their orbital programs to calculate the path of a black hole through the earth. When you radioed your results from yesterday to CIA headquarters, Isaacs relayed the essence of it to me. I'd calculated so many orbital eccentricities that I was getting a bit eccentric myself. I'm afraid I was rather obvious about my desire to be out here where the action is, even though that wasn't on the programme. Lord knows I'll just be a fifth wheel.'

'In any case,' continued Runyan, 'I was picked up by an Air Force plane this morning and, much to my pleasant surprise, met Pat here in Yuma.'

'Well, I'm glad to see you both,' admitted Gantt. 'I confess I've been bothered by not having anyone here to talk to about this business. How are your calculations going?' he asked Runyan.

'The model basically fits the data. But there are lots of loose parameters. We don't know enough about the detailed structure of the inner earth and how a small black hole would interact with it to predict small subtle shifts in the orbit with any degree of confidence. A little extra rock, like the roots of a mountain range, can perturb the orbit slightly, depending on angle of approach, a bunch of things. You can get slow cumulative effects, or an occasional finite perturbation. Hard to pin down. The data you're collecting now should allow us to fix some of those parameters. That still won't be the same as proving my picture is right.'

'Actually,' interjected Gantt, 'if we are going to discuss this matter, and I surely want to, we should move over to my tent. It's a little less public there.'

They picked up their drinks and moved off to Gantt's tent which was set off somewhat from the main compound. Gantt went off to gather up two more folding chairs and returned to arrange them in the small patch of shade available.

'Have you learned anything new?' he inquired of Danielson.

'I've collated some more data from the Large Seismic Array and various other monitoring stations. There have been some refinements in our estimations, but nothing qualitatively new.' She took a sip other tea. 'In fact, there's been one major frustration. We had hoped to get the Navy to make systematic measurements of the sonar signal. That would have given us much better positions. Unfortunately, their old data isn't much good now, and they couldn't or wouldn't respond fast enough to get any new data this last week. As a result, the measurements of positions you got yesterday are probably the best we have.'

'Did you explain Alex's hypothesis to the Navy?' Gantt wanted to know.

'No,' replied Danielson, 'the decision was made not to spread that notion any further than necessary until the results of this expedition are in.' She leaned towards Gantt. 'What about this cessation of the signal below the surface which you reported yesterday? My data have never shown a signal from the upper mantle, but you reported a definite time delay. That would be a small effect.in my data which has poor time resolution, but it might be present. I didn't have time to look carefully before hopping the plane. Don't you think it's reminiscent of the sonar signal stopping at the surface of the ocean, just that it starts earlier and lasts a bit longer?'

'Yes, that's my impression,' said Gantt. 'It's strange behaviour for a normal seismic wave, but it might be consistent with Alex's beast as we discussed a La Jolla.' He paused to scratch his head and shuffle his toe in the dirt. 'Still, I can't help wondering whether we could be dealing with some special fissuring that focused normal seismic waves, and those fissures could terminate below the surface.'

'But that wouldn't explain the delay in the return of the waves,' Runyan pointed out, 'nor the holes drilled in Nagasaki and Dallas.'

'Well, maybe the energy is temporarily stored as a mechanical stress in the rock and then released. I admit I don't have a real physical picture of such a process, but neither do I see how to rule out the possibility. The holes? Well, you're right: I can't account for them easily either. Coincidental imperfections in the concrete?'

This rhetorical question went-unanswered. There was silence for a moment, broken by Runyan. 'As I understand from Isaacs, you had a marginal detection of an abnormal acceleration?'

'Yes,' replied Gantt, 'there was some indication in the first event. It could be real, or just an accidental accumulation of noise.'

'From the distances you got yesterday,' Runyan continued, 'what do you estimate for the location of this event coming up today?'

'My best guess is that the epicentre, if you can call it that, will be about a quarter of a mile to the northeast of here, but there's an uncertainty of a few hundred metres.'

'Hmmm, too bad we don't have that Navy sonar data,' Runyan muttered. 'I'd hate to have this thing fly up my ass.' He caught himself and turned to Danielson, patting her on the arm. 'Pardon me, hon, excuse my language.' She suppressed a smile. He turned back to Gantt.

'And you expect it at about 2:03 this afternoon?'

'Give or take a few seconds.'

'So it surfaced almost half an hour ago in northwest Louisiana ,' mused Runyan. 'It's passed through the core and is now headed up to a point in the East Crozet Basin in the southern Indian Ocean. And, after another quick pass through the core, it will soon be here.' He stared down at the brown dirt and scrubby grass beneath his feet, as if by concentrating he could peer into the depths of the earth in reality as he could by imagination and thereby witness this rogue particle at work.

'You think you're right, don't you?' Gantt inquired.

'I'm afraid I am,' Runyan answered.

Gantt stared at Runyan and then removed his glasses and wiped sweat from his eyes. 'Let me give you a tour,' he said and led his guests to the main tent where he explained the function of the arrayed instrumentation.

At fifteen minutes before two, Gantt had Runyan and Danielson stand aside while he made final preparations. Danielson glanced at her watch at two minutes after the hour just as Gantt turned to announce:

'Come and look — I'm getting a signal on the seismometers.' Runyan and Gantt approached and peered over his shoulder. All three seismometers were showing a definite increase in activity. Gantt turned to the computer, fingered the keyboard, and examined the screen.

'I'm getting a good reading on the distance, but I'm having some trouble determining exactly where it's heading since, as predicted, it seems to be right beneath us.'

They turned their attention back to the seismometers which were by now showing great activity.

'Look at this!' exclaimed Gantt. He pointed to the readings on the gravimeters. All were showing a definite and growing anomalous acceleration. Once more, Gantt swivelled in his seat towards the computer, but before he could key in his instructions, confusion erupted.

Runyan first saw the needle of the seismometer in the camp go off scale, slamming against its restraining pin. Before his mind could quite absorb the implication of that occurrence, his body recorded a rapid, bizarre set of feelings. First, he had the definite sensation that the floor of the tent had accelerated upward suddenly like an express elevator. This feeling was terminated by a sideways impulse as if he had been hit with a sudden, strong gust of wind. Just as quickly, that sensation was replaced by a familiar fearsome tickle in stomach and gonads. Runyan was reminded of a roller coaster as it begins its first terrifying descent, leaving tender organs in the grasp of inertia. His ears registered a sucking whistle, rapidly diminishing in amplitude as if someone had turned on a vacuum cleaner just outside the tent and then whisked it rapidly away.

As these sensations passed, Runyan became aware of chaotic shouts beginning to echo around the camp and of Danielson half sprawled, grasping the back of Gantt's chair. Danielson had taken a step towards Gantt and had been caught with one foot m the air when she was bumped sideways and knocked off balance. Runyan helped Danielson regain her feet. She collapsed against him, weak— kneed and pale with shock. Runyan held her shoulders gently.

The whistling noise returned, this time not quite so loud and at a higher pitch. Danielson stepped back from Runyan, her hands on his chest, her eyes searching his for explanation, confirmation. After a moment, Runyan looked towards the instrumentation. Danielson's gaze followed his and they simultaneously swivelled to look at the seismometers. All needles had fallen to rest, tracking a straight line down the centre of the strip charts. In the same instant as the faint whistling stopped, the needles witched and once more the one on the camp instrument slammed against its restraining pin. As they watched, the needles began to swing, first entirely across the chart and then with gradually diminishing amplitude.

The hoarse voices outside the tent died with the swing of the needles, and Runyan spoke first.

'Goddamn!' he said with measured stress. And then again, 'Goddamn!'

As the reaction began to sink in, he felt his legs begin to shake. He moved uncertainly to the nearest chair and collapsed in it. He looked at Gantt, whose face was ashen, and at Danielson who, by contrast, was beginning to regain some colour. Her eyes now showed the intensity of contained excitement. She suddenly had an idea, turned and rushed out of the tent. The two men sat in silence until one of Gantt's assistants burst in.

'Dr Gantt,' he shouted, 'what'n hell was that?'

Gantt turned and looked at him for a long moment before replying, 'I don't know, an earthquake, I suppose.'

'Hell, that wasn't like any earthquake I've ever been in,' replied the other, his voice barely quieter. 'Two fellows just outside the tent got knocked on their butts. I was a hundred yards away and didn't feel a thing. And that noise, I've never heard a quake make a noise like that!'

'It was somewhat irregular,' Gantt conceded. 'Why don't you check out the camp and the other sites to see if everything is all right. I'll see what I can figure out from the data we collected.'

The man knew he was being put off, but could see nothing to do about it. He paused a moment until it was clear that Gantt had nothing further to say, then departed with an aggressive stride, nearly colliding with Danielson, who rushed in as he left.

She hurried across the tent floor and pulled up a chair to sit at right angles to Runyan. His arm was draped on the chair. Danielson grasped his hand in both of hers and gave it a strong, almost painful, squeeze.

Barely aware of Danielson beside him, squeezing his arm, Runyan was caught up in a maelstrom of fragmentary thoughts. He couldn't grasp the details: they moved too fast, too lightly, wafted away like floating cottonwood seeds if he tried to grab at them. Somehow, though, he caught enough glimpses through the swirl. Us? Them? He couldn't see who, but he knew the answer.

'You were right, Alex,' Danielson said in a tense hissing whisper. 'I don't see any sign of a tunnel outside the tent, but I know you were right. That force! It could only have been the gravity! It is a black hole!' As she said the last words she raised his hand in hers and banged it back down on the arm of the chair. Runyan winced slightly.

Danielson had been looking at his face without seeing. As the grimace passed briefly over Runyan's features, she suddenly became cognizant of the black desolation reflected there. She stared at his impassive face as her own tenseness and excitement abated. She turned her head to look briefly at Gantt and read the same feeling of devastation on his face. Her mind spun with conflicting emotions as she released her grip on Runyan's slack hand and slumped back in her chair.

My god, she thought, it's like being torn apart, elation and terror at the same time. She recognized that she had been completely committed to this project, that she craved for her passion to be justified. The frightening encounter had been so real, so visceral, she felt — vindicated! But something in her mind cowered like a timid creature, beset by a raging beast. Her mind froze, resisting the full implications of what had transpired here. Where had it come from? What were they going to do? They had done what they had come to do. But were they better off, or worse?

She grabbed at a straw. Take a step, a small step. We've get to move on.

'Professor Gantt?' she inquired. 'I've got to call Bob Isaacs.'