"In addition, if you go to the site of the crash even today and dig down about fifty feet it is possible to find pieces of airframe and engine. We have done that; it will take another day to completely sift the ground for a radius of three miles from the impact site, but the outlook for finding the stunner is not good. I will keep you posted on the results.

"The most promising avenue, naturally, is with the FAA investigators. We are looking into their subsequent lives minutely. There is still a chance that someone who went to the crash site picked up the stunner and carried it away -- indeed, if we don't find it in our digging, we must assume that someone did so. The problem, of course, is that the wreckage has been lying there for fifty thousand years, and the stunner could have been taken during any of the twenty-six billion minutes that have elapsed since that time."

I wondered why I'd ever liked him. The bastard was showing off. Facts at his fingertips, here's what we're doing, the investigation was in good hands ... I'd never have tolerated that kind of report from one of my people for even one of those twenty-six billion minutes. But since I wasn't in charge here I merely swallowed my anger and wondered when he'd get to the important part.

"The important factor," he said, confirming my judgement of what had gone before, "is the timestream itself. All the measurements we have taken so far show the timestream has absorbed this twonky with no disturbance."

I sat back and breathed a little easier. To sum up what he'd said so far, in a less windy way: Two guns had been left behind. One of them, so far as we could tell, would probably never be found. If it wasn't, then its mere presence in the past would not be enough to upset the delicate balance of events. We were home free.

Even if someone did find it, it did not necessarily mean disaster. It could have been rendered inoperative in the crash, in which case it was just an odd hunk of plastic and other junk. It might raise a few eyebrows, but nothing more. We could live with raised eyebrows.

We speak of the rigid framework of events, but the fact is there is some leeway.

Apparently things tend to happen the way they should happen, according to whatever plan was dictated by whoever's in charge of this stinking universe. Changes, if they are minor, correct themselves in ways no one understands but which tend to make a hash of anybody's theory of free will.

Picture an Indian passing through the site of the 1955 crash, many years later. He stumbles over Pinky's lost weapon -- broken, useless, but something that shouldn't have been there. He picks it up, scratches his head, and tosses it away.

If the universe were absolutely rigid then we'd be sunk: The time he wasted picking up the gun and throwing it away would change his life minutely, but the change would reverberate through time, growing larger with each passing year.

You could imagine any chain of events you wanted to.

The Indian gets back to his teepee five seconds later than he would have. The phone is ringing but he just misses a call he would have gotten if he hadn't stopped for the gun. (Do teepees have phones? Did Indians still live in them in 1955? Never mind.) If he'd gotten the call he'd have jumped on his horse and ridden into town and been struck by a car-driven by a guy who was on "his way to murder someone but now had to deal with a dead Indian -- so the guy who would have died didn't die, with the result that in a few years he'd discover a cure for a type of cancer -- which would afflict a President of the United States in 1996 -- so the President would be cured instead of dying when he should have died -- and a war would happen that shouldn't have happened.

If it worked that way we wouldn't be able to make time snatches.

But the way it really works leaves us a loophole. There are two salient facts to keep in mind: One: Things can be taken from the past as long as reasonable substitutes are left in their place.

Two: Events tend toward their predestined pattern.

Suffering from an energy shortage? Why not use the Gate to go back to 5000 B.C. and swipe a trillion barrels of crude oil out from under Saudi Arabia before there is any such thing as an uppity oil sheik? Fine. No sweat. Just as long as you replace it with a trillion barrels of crude that cannot be distinguished from the oil that was stolen.

We can only take things that will not be missed, or that can logically vanish. (Who knows how many paper dips are in a box? Who is upset if one carton of cigarettes is missing out of a shipment of 10,000? A rational person assumes petty pilferage if he misses it at all; I have pilfered many a carton in my day.) But it's a very strict rule. It means we can only take things from narrowly defined times and places, and if we take anything major we have to leave behind good copies of what we took.

So if somebody is about to die and no one will ever see him alive again, why not kidnap him while he's still alive and leave in his place a wimp that is indistinguishable from the dead body he was about to become? Rule two makes that possible. The copy is not going to be exact, not down to the genetic level, not down to the sub-atomic level. It's going to weigh a few ounces more or less than the original. There will always be subtle differences, but the universe adjusts to them, short of a critical threshold.

And so we snatch.

But beyond these small, acceptable changes, things get very risky indeed.

The generic description for the trouble we were afraid of is "The Grandfather Paradox."

Simply stated, I go back in time, do something foolish, and as a result my grandfather dies at the age of eight. That means he never met my grandmother, and my father was never born, and I was never born. The paradox is that if I was never born, how did I go back and kill my grandfather? Nobody knows for sure. Theories about the Gate abound, some of them contradictory, but it is generally accepted that the universe readjusts along the simplest lines. It shifts around in some multidimensional fashion, and when it's through, no time machine ever existed. My grandfather lived, and my father was born because I never went back to fool with causality.

What that would mean to me, I don't know. Probably I'd have been a drone, laughing it up, having a great time, and finally learning to skydive. My entire life has been lived around the Gate. I have difficulty imagining myself without it.

On the other hand ...

(And there's always another hand in Time Travel ... ) My people did not invent the Gate. It's been sitting right where it is for thousands of years as civilizations grew up and fell around it.

We believe it was invented by humans, but we can't look into that time, obviously, since the Gate was in operation then.

And something happened to those people.

I wish I knew what. Possibly they got so scared of what they were fooling with they just turned if off and left it there, afraid or unable to destroy it, and wandered off into the desert.

We do know that the end of the First Gate Civilization coincided with a big war and a dark age. The survivors didn't write history books." It's the biggest gap between my time and the twentieth century.

People from my time have gone back to that era of the first Gate shutdown. So many of them that it is useless to scan it; the period is riddled with the blank spots of temporal censorship.

And none of them ever came back.

Perhaps this is tied up with causality and the Grandfather Paradox, but the connection is beyond me.

The point is, if the Gate had never existed I would be living in a very different world.

Possibly a better one, but it's more likely it would be worse. How could it be worse? Easy.

The Last Age could have been three or four thousand years ago instead of right now. The human race could already be extinct instead of just racing toward oblivion. It's sort of miraculous that we've lasted as long as we have.