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?'