Garwood sighed. "I should have known you wouldn't buck your orders," he said bitterly.

"And leave you out here, threatening a community of innocent bystanders?" Davidson retorted, feeling oddly stung by the accusation. "I have a working conscience, Doctor, but I also have a working brain.

Backdrop is still the safest place for you to be, and you're going back there. End of argument." Abruptly, he got to his feet. "Come on. I'll have some of my people pack up your stuff and bring it to Backdrop behind us."

Reluctantly, Garwood also stood up. "Can I at least ask a favor?"

"Shoot."

"Can we drive instead of flying? I'm still afraid of what influence I might have on a plane's engines."

"If you can sit this close to that terminal without killing it, the engines should be perfectly safe," Davidson told him.

"Under the circ.u.mstances, 'should' is hardly adequate*"

"You're arguing in circles," Davidson pointed out. "If you get killed in a plane crash, how is anyone going to use your equations to build a time machine?"

Garwood blinked, then frowned. "Well... maybe I wouldn't actually die in the wreck."

"All right, fine," Davidson snapped, suddenly tired of the whole debate. "We'll put an impact bomb under your seat to make sure you'll die if we crash. Okay?"

Garwood's face reddened, and for a second Davidson thought he would explode with anger of his own.

But he didn't. "I see," he said stiffly. "Very well, then, let's find a phone booth and see what Saunders says. You will accept suggestions from Saunders, won't you?"

Davidson gritted his teeth. "Never mind. You want to sit in a car for fourteen hours, fine. Let's go; we'll radio Chanute from the car and have them call in the change of schedule to Backdrop. And arrange for a quiet escort."

V.

"I hope you realize," Garwood said heavily, "that by bringing me back you're putting everyone in Backdrop at risk."

Saunders raised polite eyebrows. Polite, stupidly unconcerned eyebrows. "Perhaps," he said. "But at least here we understand what's going on and can take the appropriate precautions. Unlike the nation at large, I may add, which you've just spent nearly four months putting at similar risk. Under the circ.u.mstances, I'm sure you'd agree that one of our concerns now has to be to keep you as isolated fromthe rest of the country as possible." He shrugged. "And as long as you have to be here anyway, you might as well keep busy."

"Oh, of course," Garwood snorted. "I might as well help Backdrop to fall apart that much soo*"

He broke off as a m.u.f.fled cracking sound drifted into the room. "More of the plaster going," Saunders identified it off-handedly. "Nice to hear again after so long."

Garwood felt like hitting the man. "d.a.m.n it all, Saunders," he snarled. "Why won't you listen to reason? A working time machine cannot be made. The very fact that Backdrop is falling apart around me*"

"Proves that the machine can be made," Saunders cut him off. "If you'd stop thinking emotionally for a minute and track through the logic you'd realize that." Abruptly, all the vaguely amused patience vanished from his face, and his eyes hardened as they bored into Garwood's with an unexpected intensity. "Don't you understand?" he continued quietly. "When you left, the probability-shift damage to Backdrop dropped off to near zero. Now that you're back, the destruction is on the increase again."

"Which is my point*"

"No; which is my point," Saunders snapped. "The probability-shift effect cannot exist if a working time machine isn't possible."

"And yet that same effect precludes the manufacture of any such machine," Garwood pointed out. "As I've explained to you at least a hundred times."

"Perhaps. But perhaps not. Even given that the concept of time-travel generates circular arguments in the first place, has it occurred to you that a working time machine might actually prove to be a stabilizing factor?"

Garwood frowned. "You mean that if we have the theoretical capability of going back and correcting all these alterations of history then the wild fluctuations will subside of their own accord?"

"Something like that," Saunders nodded. "I did some preliminary mathematics on that question while you were gone and it looks promising. Of course, we won't know for sure until I have all the equations to work with."

"And what if you're wrong?" Garwood countered. "What if a working time machine would simply destabilize things further?"

A flicker of Saunders's old innocent expression crossed the man's face. "Why, then, we won't be able to make one, will we? The components will fall apart faster than we can replace them."

"In which event, we're back to the probability-shift effect being a circular paradox," Garwood sighed. "If it prevents us from building a time machine, there's no time travel. If there's no time travel, there's no change in probabilities and hence no probability-shift effect."

"As I said, time travel tends to generate paradoxes like that." Saunders pursed his lips. "There's one other possibility that's occurred to me, though. The man who brought you back from Champaign*Major Davidson*said in his report that you'd been trying to find an alternative solution to the time travel equations. Any luck?"

Garwood shook his head. "All I found was blind alleys."

"Maybe you just didn't get to look long enough."Garwood eyed him. "Meaning...?"

"Meaning that one other possible explanation of the probability-shift effect is that there is indeed another set of solutions. A set that will let us build the machine and still be able to go back and change things."

Garwood sighed. "Saunders... don't you see that all you're doing is just making things worse? Isn't it bad enough that things fall apart around me?*do you want to see it happening on a global scale?

Stabilization be d.a.m.ned: a time machine*a real, functional time machine*would be the worst instrument of destruction ever created. Ever created."

"All I know," Saunders said softly, "is that anything the universe allows us to do will eventually be done.

If we don't build the machine, someone else will. Someone who might not hesitate to use it for the ma.s.s destruction you're so worried about."

Garwood shook his head tiredly. The discussion was finally turning, as he'd known it eventually would, onto ail-too familiar territory: the question of whether or not the fruits of Backdrop's labor would be used responsibly by the politicians who would inherit it. "We've gone round and round on this one," he sighed, getting to his feet. "Neither of us is likely to change the other's mind this time, either. So if you don't mind, it's been a long drive and I'd like to get some rest."

"Fine." Saunders stood, too. "Tomorrow is soon enough to get back to work."

In the distance, the sound of more cracking plaster underlined his last word. "And if I refuse?" Garwood asked.

"You won't."

"Suppose I do?" Garwood persisted.

Saunders smiled lopsidedly and waved a hand in an all-encompa.s.sing gesture. "You talk too contemptuously about the not-me' generation to adopt their philosophy. You won't turn your back on a problem this serious... especially given that it's a problem partially of your own creation."

For a long moment Garwood considered arguing the latter point. It had been Saunders, after all, who'd pushed Backdrop into existence and then dragged him into it.

But on the other hand, it wasn't Saunders who knew how to build the d.a.m.n time machine.

Wordlessly, he turned his back on the other and headed for the door. "Rest well," Saunders called after him.

His office, when he arrived there the next morning, was almost unrecognizable.

Two pieces of brand-new equipment had been shoehorned into the already cramped s.p.a.ce, for starters; a terminal with what turned out to be a direct line to the Minneapolis Cray HI supercomputer lab, and an expensive optical scanner that seemed set up to read typewritten equations directly onto the line. So Saunders is capable of learning, Garwood thought sardonically, careful not to touch either instrument as he gave them a brief examination. The electronic blackboard that had fallen apart shortly before he left Backdrop was gone, replaced by an old-fashioned chalk-on-slate type, and his steel-and-plastic chair had been replaced by a steel-and-wood one. Even his desk looked somehow different, though it took him a long minute to realize why.All the piles of papers had been changed.

Silently, he mouthed a curse. He hadn't expected the papers to remain untouched*Saunders would certainly have ransacked his desk in hopes of finding the rest of his time-travel equations*but he hadn't expected everything to get so thoroughly shuffled in the process. Clearly, Saunders had gone about his task with a will and to h.e.l.l with neatness; just as clearly, it was going to take most of the day to put things back where he could find them again. With a sigh, he sank gingerly into his new chair and started restacking.

It was two hours later, and he was not quite halfway through the task, when there was a knock on the door. "Come in, Saunders," he called.

It wasn't Saunders. "h.e.l.lo, Dr. Garwood," Major Davidson nodded, throwing a glance around the room.

"You busy?"

"Not especially." Garwood looked up at him. "Checking to make sure I'm still here?"

Davidson shrugged fractionally, his gaze steady on Garwood. "Not really. I believe Colonel Bidwell has been able to plug the hole you got out by the last time."

"I'm not surprised." The look in Davidson's eyes was becoming just the least bit unnerving. "May I ask why you're here, then?"

Davidson pursed his lips. "The random destruction has started up again since we got in last night."

"This surprises you?"

Davidson opened his mouth; closed it. Tried again. "I'd... rather hoped you weren't so clearly the pivotal point of the effect."

"I thought we'd discussed all that back in Champaign," Garwood reminded him. "I'm the only one who knows how to build the machine, so of course the probability-shift effect centers around me."

Davidson's eyes flicked to the computer terminal/optical scanner setup. "And Saunders wants you to let him in on the secret."

"Naturally. I don't intend to, of course."

"And if he doesn't give you that choice?"

"Meaning...?"

"Meaning he tried once to use hypnosis to get your equations out of me. With you, the method would probably work."

Garwood's mouth felt dry. "He knows better than to try something that blatant," he said. Even to himself the words didn't sound very convincing.

"I hope so. But if he doesn't... I trust you'll always remember that there's at least one other person in Backdrop who recognizes the danger your knowledge poses."

Garwood nodded, wishing he knew exactly what the man was saying. Was he offering to help Garwood escape again should that become necessary? "I'll remember," he promised. "You're going to be here for awhile, then?"Davidson smiled wryly. "They let me out on a tight rein to go after you, Doctor. That doesn't mean they want me running around loose with what I know about Backdrop. I'll be on temporary duty with the security office, at least for the foreseeable future." He paused halfway through the act of turning back toward the door. "Though I don't suppose the term 'foreseeable future' has quite the same meaning as it used to, does it?"

Without waiting for an answer, he nodded and left. No, it doesn't, Garwood agreed silently at the closed door. It really doesn't.

He thought about it for a long minute. Then, with a shiver, he turned back to his papers.

One by one, the leads faded into blind alleys... and two months later, Garwood finally admitted defeat.

"d.a.m.n you," he muttered aloud, slouching wearily in his chair as far away from his terminal as s.p.a.ce permitted. "d.a.m.n you." An impotent curse hurled at the terminal, at the program, at the universe itself.

"There has to be a way. There has to be."

His only answer was the vague and distant crash of something heavy, the sound m.u.f.fled and unidentifiable. A piece of I-beam from the ceiling, he rather thought*the basic infrastructure of Backdrop had started to go the way of the more fragile plaster and electronics over the past couple of weeks. Saunders had spent much of that time trying to invent correlations between the increase in the destruction with some supposed progress in Garwood's mathematical work, and he'd come up with some highly imaginative ones.

But imaginative was all they were... because Garwood knew what was really happening.

Perversely, even as it blocked his attempts to find a safe method of time travel, the universe had been busily showing him exactly how to transform his original equations into actual real-world hardware.

It was, on one level, maddening. He would be sitting at his typewriter, preparing a new set of equations for the optical scanner to feed into the computer, when suddenly he would have a flash of insight as to how a properly tuned set of asynchronous drivers could handle the multiple timing pulses. Or he'd be waiting for the computer to chew through a tensor calculation and suddenly recognize that an extra coil winding superimposed on a standard transformer system could create both the power and the odd voltage patterns his equations implied. Or he'd even be trying to fall asleep at night, head throbbing with the day's frustrations, and practically see a vision of the mu-metal molding that would distort a pulsed magnetic field by just the right amount to create the necessary envelope for radiating plasma bursts.

And as the insights came more and more frequently*as a working time machine came closer and closer to reality*the environment inside Backdrop came to look more and more like a war zone.

Across the room the terminal emitted a raucous beep, signaling the possibility of parity error in its buffer memory. "d.a.m.n," Garwood muttered again and dragged himself to his feet. Eventually he would have to tell Saunders that his last attempts had gone up in the same black smoke as all the previous ones, and there was nothing to be gained by putting it off. Picking up his hardhat, he put it on and stepped out of his office.

The corridor outside had changed dramatically in the past weeks, its soothing pastel walls giving way to the stark metallic glitter of steel shoring columns. Senses alert for new ripples in the floor beneath him as well as for falling objects from above, he set off toward Saunders's office.Luck was with him. The pa.s.sages were relatively clear, with only the minor challenge of maneuvering past shoring and other travelers to require his attention. He was nearly to Saunders's office, in fact, before he hit the first real roadblock.

And it was a good one. He'd been right about the sound earlier; one of the steel I-beams from the ceiling had indeed broken free, creating a somewhat bowed diagonal across the hallway. A team of men armed with acetylene torches were cutting carefully across the beam, trying to free it without bringing more down.

"Dr. Garwood?"

Garwood focused on the burly man stepping toward him, an engineer's insignia glittering amid the plaster dust on his jumpsuit collar. "Yes, Captain?"

"If you don't mind, sir," the other said in a gravelly voice, "we'd appreciate it if you wouldn't hang around here any longer than necessary. There may be more waiting to come down."

Garwood glanced at the ceiling, stomach tightening within him as he recognized the all-too-familiar message beneath the other's words. It wasn't so much interest in his, Garwood's, safety as it was concern that the cloud of destruction around him might wind up killing one of the workers. Briefly, bitterly, Garwood wondered if this was how Jonah had felt during the shipboard storm. Before he'd been thrown overboard to the whale... "I understand," he sighed. "Would you mind pa.s.sing a message on to Dr.

Saunders when you have the chance, then, asking him to meet me at my office? My phone's gone out again."

"A lot of 'em have, Doctor," the engineer nodded. "I'll give him the message."

Garwood nodded back and turned to goAnd nearly b.u.mped into Major Davidson, standing quietly behind him.

"Major," Garwood managed, feeling his heart settle down again. "You startled me."

Davidson nodded, a simple acknowledgment of Garwood's statement. "Haven't seen you in a while, Dr.

Garwood," he said, his voice the same neutral as his face. "How's it going?"

Garwood's usual vague deflection to that question came to his lips... "I have to get back to my office," he said instead. "The workmen are worried about another collapse."

"I'll walk with you," Davidson offered, falling into step beside him.

Davidson waited until they were out of sight of the workers before speaking again. "I've been keeping an eye on the damage reports," he commented in that same neutral tone. "You been following them?"

"Not really," Garwood replied through dry lips. Suddenly there was something about Davidson that frightened him. "Though I can usually see the most immediate consequences in and around my office."

"Been some extra problems cropping up in the various machine and electronic fabrication shops, too,"

Davidson told him, almost off-handedly. "As if there's been some work going on there that's particularly susceptible to the Garwood Effect."

Garwood gritted his teeth. The Garwood Effect. An appropriate, if painful, name for it. "Saunders has had some people trying to translate what little he and the rest of the team know into practical hardware terms," he told Davidson."But they don't yet know how to build a time machine?"

"No. They don't."