He sat suddenly next to Rutherford and continued.

'I had some of my people keeping an eye on it, even though we didn't know what to make of it.'

Then he was thinking out loud.

'The seismic data only told us what was happening in rock. I convinced myself that whatever it what was confined to the earth's crust, that the seismic waves were its essence. Now you tell me something about it continues into the water.' He shook his head. 'I don't like it. I don't like this at all.

'Listen, we've learned some things you apparently haven't stumbled onto yet. This thing is always there, and very methodical. It just goes back and forth, back and forth, always on the same path through the earth.' He waved his arms. 'And then out into the ocean! Shit! No reason to think it doesn't continue into the atmosphere! No telling how far it goes.'

He leaned back against the wall. 'Our problem is that McMasters scuttled our operation, claimed it wasn't Agency business.' He paused for a moment. 'Damn, it's hot in here! Let's go someplace where we can do a little serious talking. Better make it your office, since the subject is officially verboten on my turf.'

As Rutherford steered his staff car through the prerush hour traffic, Isaacs explained animatedly how his interest in the seismic signal became aroused during his duty at AFTAC. He then outlined the progress Danielson had made, culminating in her conclusion that the phenomenon followed a trajectory fixed in space. They finished the drive in silence while Rutherford ruminated on this new information.

A half hour later they entered Rutherford 's office. Rutherford ordered up the Navy file on the acoustic phenomenon. He sat behind his desk while Isaacs remained standing, rocking nervously on the balls of his feet. Rutherford spoke first.

'Boy, I'm really having trouble absorbing this. I had a notion of a random, infrequent occurrence, and now you describe something punching through the surface like clockwork, every eighty minutes or so. I guess I still don't get the picture. Tell me again how this fixed motion works.'

'Let me use this globe,' Isaacs said as he lifted a fancy relief model of the earth off its shelf and put it on Rutherford 's desk. He grabbed a pencil and held it pointed towards the surface of the globe, about a third of the way above the equator. 'The thing always moves along a line, like this.' He moved the pencil in and out, parallel to itself, 'Zipzip, zipzip. But as the earth turns,' he spun the globe slowly with his free hand, 'the thing always comes up in a different place.' He tapped the pencil rhythmically as he spun the globe, each tap hitting it an inch further on than the last.

'Let me see that,' said Rutherford , reaching for the pencil. He held it alongside the globe so that he could project it in his imagination into the centre of the globe. Then he moved it back and forth along its length as he spun the globe slowly, eraser to the northern hemisphere, then point to the southern, eraser to the north, point, south. 'Okay, I think I get the picture, but what could possibly do that? Through the centre of the earth? Jesus Christ!'

He jerked his head up as a knock sounded at the door.

'Come in.'

An aide came in bearing a file folder.

'Bob, Lieutenant Szkada. Lieutenant, Bob Isaacs, Central Intelligence.'

Isaacs nodded at him.

'Sir.' The young man placed the folder on Rutherford 's desk.

'That'll be all,' Rutherford said to him with a note of paternalism.

'Yes, sir.' The lieutenant turned and left.

'Sharp young man, that,' Rutherford confided. 'My right arm.' He pulled the file towards him. 'Let's see what we have here.' He extracted a list of reported detections and banded it to Isaacs. Rutherford leafed through the corresponding write-ups, looking for ones that were not hopelessly sketchy.

As Isaacs scanned down the list of sonar reports, he let out a loud exclamation.

'I'll be damned!'

'What?'

'One of life's little ironies. Several of these reports are from the undersea arrays of acoustic monitors.'

'Sure, we have those babies all over, bound to pick up something like this. So?'

'That system is also operated by AFTAC. The whole ball of wax was right under my nose, both seismic and sonar data. I'm kicking myself, I was so hung up on the seismic signal propagating through the earth. I had my people trying to put together a puzzle with half the pieces missing.'

Isaacs threw the list on the desk and pulled a chair around beside Rutherford. They spent fifteen minutes checking the tune and position on earth for each of the reports and converting that data into a projected position on the celestial sphere, to see what stars were overhead. As near as they could tell, it was always the same patch of stars. All the sonar events fell on the path predicted by the seismic data. Trying to estimate whether the influence was precisely at the phase which brought Danielson's seismic signal to the surface was more difficult, but the evidence they had seemed damning enough.

'So what did you say you are doing about all this?' Rutherford wanted to know.

'Not jackshit.' Isaacs described his skirmish with McMasters.

When he finished, Rutherford inquired, 'Can't you get McMasters to reopen the file, now that you have this confirmation from our data?'

'I doubt it.' Isaacs frowned in concentration and rubbed his prominent nose. He got up and paced the room. Post handball thirst nagged at him. He wished he had a cold beer.

'You've told me something new. The source of energy driving the seismic waves somehow proceeds into the ocean. That banishes my lingering suspicion that we were dealing with an ordinary, if highly regular, seismic phenomenon. But we're no closer to understanding what's really happening. Without a more substantial change in the situation, McMasters would stand to lose face if he backs down. I've got to have something beyond the fact that this thing is amphibious before I can go back to him and convince him to reopen our investigation.'

He crossed the room twice more, thinking.

'He's right that there's no obvious reason to consider this Agency business. But dammit! It's got to be somebody's business.'

Rutherford rubbed his chin. 'Is this thing dangerous?'

Isaacs stopped pacing and faced the man seated at the desk. 'Not clear, is it? Whatever it is, it makes a lot of noise that travels through rock and water. But noise alone doesn't make it dangerous.' He resumed his pacing.

'The scary part is that something is moving through that rock and water, making the noise. We haven't the faintest idea what. That doesn't make it a threat, but it sure as hell makes me nervous!'

Rutherford leaned forward on his desk, watching Isaacs perform his epicycles. 'Listen. Your seismic data were ideal to track this thing over large distances coherently and establish that it moves along a fixed direction. But with your hint of where and when to look, our sonar detections should give a higher precision. We could put a ship right on top of it and find out what we're actually up against.'

Isaacs sprawled stiffly in a chair, as if he might leap out of it again at a moment's notice. 'Actually, we could do something like that on land, too, if McMasters hadn't tied my hands,' he responded. 'You're right, though, you're in a position to proceed, and I'm not.

'There is a practical point,' Isaacs continued. 'As it stands now, you don't formally have enough information to move on your own. You need our knowledge that it behaves in a systematic way.'

Rutherford nodded his assent.

'But I can't give it to you officially because of this roadblock McMasters has thrown up.'

Isaacs smiled and leaned forward in his chair. 'I think you're going to have to wake up in the middle of the night with a sudden insight. Your past brilliant record would presage such a breakthrough.'