Curly had arrived last Thursday at the launch site at Tyuratam along with the laser components. Since then Curly had been working sixteen-hour days, just like Isaacs's team. The launch of the new laser could be as soon as next month. Curly was on the front line down there, beating himself and his crew to greater effort. In his room, in the bowels of this building, and in many others, thousands of American intelligence people focused on the same event. When would the launch be? What were the capabilities of this new laser? Could it be stopped? Should it be stopped? Would it strike? Where? Were there defensive measures?

Isaacs shoved his rolled cuffs further up his arms, then raised his arms in a stretch over his head. He looked at the bedraggled group around him. Martinelli sat with one of his aides in a circle of coffee cups and cigarette butts. They were sorting the latest pile of useful photographs culled from the reams that poured in from a host of satellites. Bill Earls huddled with Pat Danielson at the far end of the table. Bill had isolated the crates which housed the laser components from among the bewildering array of associated rocket parts. The task now was to glean every scrap of information they could as the relevant crates were unpacked and their contents incorporated into the rocket.

Danielson ran liaison with the computer. When Saris found some shred of evidence in a portion of one photograph, Danielson or one of her cohorts would dash off to retrieve that part of the photo from the computer memory and run it through a panoply of analysis routines, reducing noise, heightening contrast, pulling this feature then that from data, until they could do no more. Then they would move to another photo or call to Martinelli to order up a new one, concentrating on whatever feature seemed likely to be particularly illuminating. The Russians knew they were being spied upon. When they could not avoid exposing a piece, they would sometimes move it about at random, specifically to foil analysis teams. Then Isaacs's group would race to see if they could relocate the missing component, all the while searching for new clues.

Boswank had gone off to attend to other concerns. Several of his deputies remained, continually updating a list of target material amenable to investigation by clandestine networks on the ground. They conferred often with Henry Sharbunk, the representative from the National Security Agency, where a similar emergency operation progressed.

Isaacs looked again at the box Curly was operating on. If it held a power supply, as Bans maintained, what would that tell them? How the hell could they learn anything useful if they didn't know what it powered? He had a strong urge to shout down at Curly, to force him to turn his face up, so he could see him, talk to him. Demand to know where he intended to install that box, what it would do.

He snapped out of this fantasy when he felt a gentle hand on his shoulder. He looked up into Kathleen's eyes. She was deeply sombre. He looked down at the note in her hand and took it from her. His chest constricted and his stomach felt a wince of sympathetic nausea. He had been expecting this, but he sickened anyway. Ed Jupp was dead.

Isaacs dropped his head onto his hand, replaying in his thoughts a fortnight of increasing agony. He had never met the man, but followed the progress, through messages such as these, as his hair fell out and the pain turned his guts to liquid fire.

Isaacs finally looked up at Kathleen and nodded to her. She gave his shoulder a brief, hesitant pat, and then left.

Isaacs finally cleared his throat and raised his voice above the hubbub of muted conversations.

'Excuse me!' He waited until he had their attention. 'I just got a note from Walter Reed Hospital. Major Edward Jupp died an hour ago from radiation poisoning.'

Everyone in the room lowered their eyes from Isaacs and did little things with whatever objects lay immediately in front of them.

'It's late Sunday. None of us have seen our families in a while. We've accomplished a lot in the last few days, and this rocket's not going anywhere,' he gestured at the photograph of Curly before him. 'Let's break and get a good night's rest. We'll hit it again tomorrow.'

A riffle of shuffling and glances passed around the table. Despite the fatigue, putting down such an all-consuming task was not easy. Finally Martinelli spoke.

'Damn good idea. I came just that close to ordering up a new photo of the grounds in my coffee cup.' He turned to his aide. 'Let's just leave these in the piles as we have them,' he pointed at the stacks of sorted photographs. 'Lord knows there'll be a fresh batch tomorrow.' He got up and stretched.

Slowly the other groups around the table began to arrange their material so that they could pick up again in the morning. They filed out one at a time, disoriented by the need to cease the intense effort and think of home and rest. Isaacs sat staring at the top of Curly's head. He finally realized that everyone had left but Danielson. She moved over and sat down next to him.

'I'm sorry about Jupp,' she said, her voice throaty. Isaacs nodded and looked at her, not quite seeing. Finally she spoke again. 'Do you have enough energy to give me some advice?'

Isaacs rubbed his eyes with the palms of his hands and worked his shoulders. 'I can try.' He gave her a wan smile. 'I have this vague feeling I'm not at the peak of efficiency.'

Her voice was apologetic. 'I'm sorry to trouble you, but I have a conflict. Maybe you can help me resolve it. I've been spending a fair bit of time on that seismic signal you asked me to investigate. I had to drop that when this rush came up, of course. The problem is the people I've been working with at the Cambridge Research Lab. They know I've got an emergency down here, but they don't know what or how severe. They've assembled seismic data from a lot of universities and apparently feel there is significant new information in it, more thorough coverage. They've been pressuring me to go back up and work on it, as I originally promised. I don't quite know what to tell them. Should I tell them to put the whole flung on indefinite hold? Should I try to get up there for a little while if we can see a break here? I'm not sure how I should respond, but I don't think I should just keep putting them off.'

Isaacs thought for a moment. His pleasant days in Florida seemed another era, another world. 'We're going to be at this until the launch, a month, six weeks, several months if they get hung up somehow. Then a different show once it's in orbit. On the other hand, we're over a hump here in terms of sorting the procedures at the launch site.' He looked at her intently. 'Saris has been particularly pleased with your work, by the way, thinks you have a real flair for isolating important ingredients in the photos.'

Danielson smiled in pleasure.

'That means you're especially valuable to us on this project, but we can't keep going with the intensity we have the last four days, and shouldn't have to. If you took a break to do something else, you might come back fresher. How would you feel about that?'

'I understand how crucial this effort is, but I'm just one member of the team and I'm still fascinated by this seismic thing.' She looked at him, searching his eyes. 'I'd hate to see it dropped.'

He pushed back in his chair. 'Let me talk to Saris. See if he thinks he can spare you. We'll have a better feeling of developments by midweek. Maybe we can work in a break for you.'

'Thank you. I'd like that. I'll hold the Lab at bay and check with you later in the week.'

She rose and left the room at a surprisingly fresh pace. Isaacs picked up the picture of Curly between his index and middle finger and sailed it gently to the middle of the conference table, a thousand dollar frisbee, one of several hundred stacked around the room. He checked that the door was locked on his way out, bid good evening to the security guard posted outside, and headed for his office, picturing a tall drink and cool, soothing sheets.

Sometime after lunch in the middle of May, Pat Danielson paced down the long central corridor which carried her through the multi-numbered interconnected buildings of MIT. She barely recalled catching the ride from the lab in Lexington into Cambridge. With little sleep in the last three days, she felt the hollow tension of deep fatigue. Atop that fundamental, like frosting on a cake, rode the giddy feeling of accomplishment that accompanies an intellectual breakthrough. That feeling provided the motive force that directed her numb legs to maintain a reasonable pace.

She crossed the main lobby decked with illustrations of ongoing student projects and pushed out the door. Pausing at the top of the steps, she blinked in the hazy sunlight. After gazing a moment at the busy traffic on Massachusetts Avenue , she leaned back against one of the tall fluted pillars and closed her eyes. Her head buzzed with the lack of sleep.

A brazen honk snapped her eyes open. She stood for a moment trying to sense if she had actually fallen asleep on her feet. Then she focused on the cab parked on the far side of the street. She gave a quick salute to the driver and proceeded down the steps where she stopped to push the walk/wait button. As the flash of red and yellow lights signalled a halt to the flow of traffic, she crossed to the taxi and climbed in the rear from the driver's side.

The driver cocked an ear and Danielson mumbled, 'Airport — Eastern shuttle.'

On the plane she tried to practise what she would say to Isaacs. Every time she began to assemble her excited thoughts into coherent English sentences, the words would drift and dissolve as her brain fought to sleep. Back in her office in the Langley headquarters she dropped her briefcase on her desk and, still standing, punched the phone for Isaacs's office.

'Yes, Miss Kate?' Isaacs fingered the intercom in answer to the buzz.

'Pat Danielson, sir. On the phone.'

'Put her on the line,' Isaacs said, reaching for his telephone. 'Hello, Pat? Isaacs, here.'

'We've completed the analysis on the periodic seismic signal,' Danielson reported. 'We've got something big, but I don't know what.' She sounded excited, only an occasional slurred word indicated fatigue.

Isaacs looked at his watch. 'It's four-thirty now, do you want to talk this afternoon, or wait until tomorrow?'

'Well, I thought you might not be free until tomorrow, but I'd rather get it off my chest. That might help me get some rest tonight. I've lived with the computer here and at the Cambridge Research Lab the last week and haven't had much sleep. I could at least give you the bottom line, then we could go into detail tomorrow sometime, after I've had a good night's sleep.'

'Okay, come on up.' Isaacs buzzed Kathleen to show Danielson in on her arrival and cleaned his desk of the latest summaries concerning the new Russian laser being readied for launch at Tyuratam.

Danielson arrived two minutes later. She looked haggard, but an intensity burned in her eyes. She dropped into the proffered chair, took a deep breath, and held it momentarily before exhaling slowly through pursed lips.

Isaacs waited for her to compose herself. Danielson's mind spun with the reams of data she'd lived with over the last few days as she endeavoured to decide where to begin.

'It's not a surface effect,' she blurted out. 'In places we can clearly track it from the mantle to the core. It then seems to head on back to the surface. A scattered wave would have an attenuated amplitude. This grows in strength as it leaves the core and passes into the mantle.'

'Does it move between two fixed points?' inquired Isaacs, already calculating the surveillance apparatus that could be used once a location was specified.

'On the contrary,' replied Danielson, destroying that train of thought. 'At first it seemed to move around randomly although confined to certain latitudes. It's too weak to follow continuously and it seemed to be taking arbitrary trajectories.

'I racked my brain trying to find a systematic effect that would tie all the data together. I only hit upon it late last night and finished working it out this morning. The path is fixed all right, but not to the earth.'

Isaacs's brows rose slightly in surprise. He didn't speak but fixed his gaze on Danielson as he waited for her to continue.

'At first I thought it always pointed in the same direction with respect to the sun. Not at the sun, but at a fixed angle to it. But that wasn't quite it, so I tried a position fixed to the distant stars and that fits like a glove, as nearly as I can tell.'

'Aaah, wait a minute,' Isaacs leaned forward on his desk and clasped his hands. 'Run that by me again.'

'Okay,' Danielson pointed her left index finger at the ceiling and moved her right index finger in a circle around it, pointed at the floor. 'As the earth rotates exactly once on its axis, marking a sidereal day, a given point on its surface will fall on the line of motion we have determined,' she moved her right finger back and forth past her left, 'and a fixed distant star will be directly overhead once more. Because of the earth's motion in orbit around the sun, the interval between times when the sun is directly overhead, the solar day, is four minutes longer. Sidereal time represents a more basic inertial clock, uncomplicated by the orbit of the earth, and that is the time this phenomenon keeps.'

'Let me get this straight,' said Isaacs. 'You're claiming that this motion is fixed in space? Just as the axis of the earth's rotation points in a fixed direction, towards Polaris?'

'Absolutely.' Danielson gave an assertive nod which caused a curl to slip down on her forehead. She pushed it back with a gesture that suddenly recalled her femininity to Isaacs, but continued at a professional clip.

'Something moves on a line through the centre of the earth. It always comes up near thirty-three degrees north latitude, goes down through the centre of the earth, and comes out again at thirty-three degrees south latitude. Then it goes back to the centre and comes out once again at thirty-three degrees north latitude. But since the earth rotates and the direction along which it moves is fixed, it never comes up at the same point twice.'

The woman's fatigue receded as she endeavoured to elaborate her argument. She jammed a slim finger onto Isaacs's desk. 'Not only is this trajectory independent of the rotation of the earth on its axis, it's also independent of the motion of the earth around the sun. We have good data now spanning three months. In that time the earth has moved one quarter of the way around the sun in its orbit, an angle of ninety degrees. Yet the seismic trajectory has pointed to the same direction in space, a point somewhat to the north and midway between the constellations of Gemini and Cancer. If you extend the line of motion through the earth's centre and out the other side, it intersects the sky at a point just south of the constellation of Capricorn.'

Danielson leaned back and looked out the window over Isaacs's shoulder, as she sought an analogy.

'It's as if there were a string tied at two opposite points in space. Cancer and Capricorn, and passing through the centre of the earth. That string intersects a different point on the earth's surface every second as the earth rotates, but the direction in which the string leads is independent of the rotation of the earth on its axis or its revolution in orbit about the sun.'

Isaacs and Danielson stared at each other and then diverted their gazes to random points in the room. Danielson, convinced of the certainty of her conclusions, nevertheless abandoned herself to retracing mentally the steps she had taken over the last few days. She hadn't the mental energy presently to contemplate the impact of her efforts. Isaacs's thoughts took two tracks simultaneously, trying to absorb the significance of the raw conclusions just presented and beginning to catalogue the possibilities for weakness or errors in the analysis leading to those conclusions.

When he spoke, Isaacs took a middle ground, that of attempting to elicit key facts. 'Tell me more about the nature of the signal itself. How close to the surface does it get? What other characteristics does it have?'

Danielson leaned back and massaged her eyes with thumb and index finger while she replied, 'Pinning down the position at a given instant is difficult because of the weak signal.' She removed her hand from her face and looked intently at Isaacs. 'Our latest estimate of the period is eighty and a half minutes, give or take a few seconds. We don't get a signal from the mantle, but then we pick it up as it proceeds back towards the core. There is also difficulty in estimating the propagation velocity without accurate positions, but it seems to pick up speed as it approaches the core of the earth. That is crudely consistent with the behaviour of an ordinary sound wave since the sound velocity goes up in the hotter parts of the core. That's about the only thing it does like an ordinary seismic wave.'

'You say that it goes right through the centre of the earth?'

'That's right. It goes down on what seems to be a straight line, then proceeds straight out to the opposite surface, always on a line pointing midway between Gemini and Cancer. As I said, it doesn't behave like a wave in the sense that a wave gets weaker as it proceeds. This may get weaker going down, but it gets stronger, if anything, on its trip up. Then, as far as we can tell, the next cycle is identical.'

Isaacs thought a moment. 'So the net power in the signal isn't changing.'

'Right again. It seems as if the strength of the signal only depends on where it is in the cycle, and that the power is the same cycle after cycle.'

Isaacs paused, then asked, 'Do you see any way this could be artificial? Man-made?'

'Not without a position fixed on the earth's surface,' replied Danielson.

'But it seems not to be a normal seismic phenomenon?' 'Too many of the properties are strange, particularly if the path is fixed in space and not with respect to the earth.'

'Could there be some tidal effect? A collective action of the sun and moon?'

'I don't see how. There's no obvious way to trigger such an event. In any case there seems to be no connection with the position of the moon which has orbited several times without changing anything while we've monitored the data. Still, we're dealing with something strange here, so possible subtle or indirect tidal effects should probably be explored.'

Isaacs fixed his gaze on the tired young woman in front of him. 'I think you're right: you're onto something peculiar,' he said slowly. 'Why don't you go home and get a good night's sleep. Come in tomorrow and we'll go into your evidence in detail.'

Danielson smiled abashedly, acknowledging her fatigue once more. 'Fine. I'll see you tomorrow morning.' She rose and let herself out the door.

Isaacs leaned back and clasped his hands behind his head, staring at the ceiling. He quickly decided he needed more information. A detailed discussion with Danielson tomorrow might show some flaw in the analysis. That was unlikely, however, despite the strange nature of the situation, considering the careful work Danielson usually produced and the sophisticated computer analysis groups on which she relied. But more information or no, this problem required expert consultation to begin even to categorize it.

He leaned forward and punched the intercom. 'Kathleen?' When she responded, he said, 'Get in touch with Martinelli. I want a one kilometre resolution photomontage of everything within ten degrees of thirty-three degrees north and south latitude and a first order scan for anything out of the ordinary. I don't know specifically what to look for.'

Isaacs then leaned back and contemplated the situation. After some time he realized that he was imagining an extra— terrestrial civilization teaming a mysterious ray at earth from some point in space. He shook his head ruefully as he put Danielson's problem out of his mind and retrieved the Tyuratam summaries from his desk drawer.