Anne nodded. "That's plain enough. It reminds me of a venetian blind that has hung up on one side. Like ours in the living room last week that I couldn't fix, but had to wait until you came home."

"Yes," said John. "Now, let us call this longer line-segment an 'alpha' universe; an analogue of our own multi-dimensional 'alpha' universe. If I move my pencil along the line at one section a second like this, it takes me ten seconds to get to the other end. We will assume that this velocity of an inch a second is the fastest anything can go along the 'alpha' line. That is the velocity of light, therefore, in the 'alpha' plane—186,000 miles a second, in round numbers. No need to use decimals."

He hurried on as Anne stirred and seemed about to speak. "But if I slide out from my starting point along a dotted line part way to the 'beta' universe—something which, for reasons I can't explain now, takes negligible time—watch what happens. If I still proceed at the rate of an inch a second in this inter-planar region, then, with the dotted lines all bunched closely together, after five seconds when I switch along another dotted line back to my original universe, I have gone almost the whole length of that longer line. Of course, this introduction of 'alpha' matter—my pencil point in this case—into the inter-planar region between the universes sets up enormous strains, so that after a certain length of time our spaceship is automatically rejected and returned to its own proper plane."

"Could anybody in the littler universe use the same system?"

John laughed. "If there were anybody in the 'beta' plane, I guess they could, although they would end up traveling slower than they would if they just stayed in their own plane. But there isn't anybody. The 'beta' plane is a constant level entropy universe—completely without life of its own. The entropy level, of course, is vastly higher than that of our own universe."

Anne sat up. "I'll forgive you this time for bringing up that horrid word entropy, if you'll promise me not to do it again," she said.

John Shrugged his shoulders and smiled. "Now," he said, "if I want to get somewhere fast, I just start off in the right direction, and switch over toward 'beta.' When 'beta' throws me back, a light-year or so toward my destination, I just switch over again. You see, there is a great deal more difference in the sizes of Alpha universe and Beta universe than in the sizes of these alpha and beta line-segment analogues. Then I continue alternating back and forth until I get where I want to go. Establishing my correct velocity vector is complicated mathematically, but simple in practice, and is actually an aiming device, having nothing to do with how fast I go."

He hesitated, groping for the right words. "In point of fact, you have to imagine that corresponding points in the two universes are moving rapidly past each other in all directions at once. I just have to select the right direction, or to convince the probability cloud that corresponds to my location in the 'alpha' universe that it is really a point near the 'beta' universe, going my way. That's a somewhat more confused way of looking at it than merely imagining that I continue to travel in the inter-planar region at the same velocity that I had in 'alpha,' but it's closer to a description of what the math says happens. I could make it clear if I could just use mathematics, but I doubt if the equations will mean much to you.

"At any rate, distance traveled depends on mass—the bigger the ship, the shorter the distance traveled on each return to our own universe—and not on velocity in 'alpha.' Other parameters, entirely under the control of the traveler, also affect the time that a ship remains in the inter-planar region.

"There are refinements, of course. Recently, for example, we have discovered a method of multi-transfer. Several of the transmitters that accomplish the transfer are used together. When they all operate exactly simultaneously, all the matter within a large volume of space is transferred as a unit. With three or four transmitters keyed together, you could transfer a comet and its tail intact. And that's how inter-planar traveling works. Clear now?"

"And that's why they call it 'stitching,'" said Anne with seeming delight. "You just think of the ship as a needle stitching its way back and forth into and out of our universe. Why didn't you just say so?"

"I have. Many times. But there's another interesting point about stitching. Subjectively, the man in the ship seems to spend about one day in each universe alternately. Actually, according to the time scale of an observer in the 'alpha' plane, his ship disappears for about a day, then reappears for a minute fraction of a second and is gone again. Of course, one observer couldn't watch both the disappearance and reappearance of the same ship, and I assume the observers have the same velocity in 'alpha' as does the stitching ship. Anyway, after a ship completes its last stitch, near its destination, there's a day of subjective time in which to make calculations for the landing—to compute trajectories and so forth—before it actually fully rejoins this universe. And while in the inter-planar region it cannot be detected, even by someone else stitching in the same region of 'alpha' space.

"That's one of the things that makes interruption of the enemy ships entirely impossible. If a ship is in an unfavorable position, it just takes one more quick stitch out of range, then returns to a more favorable location. In other words, if it finds itself in trouble, it can be gone from our plane again even before it entirely rejoins it. Even if it landed by accident in the heart of a blue-white star, it would be unharmed for that tiny fraction of a second which, to the people in the ship, would seem like an entire day.

"If this time anomaly didn't exist, it might be possible to set up defenses that would operate after a ship's arrival in the solar system but before it could do any damage; but as it is, they can dodge any defense we can devise. Is all that clear?"

Anne nodded. "Uh-hunh, I understood every word."

"There is another thing about inter-planar travel that you ought to remember," said Bristol. "When a ship returns to our universe, it causes a wide area disturbance; you have probably heard it called space shiver or the bong wave. The beta universe is so much smaller than our own alpha that you can imagine a spaceship when shifted toward it as being several beta light-years long. Now, if you think of a ship, moving between the alpha and beta lines on this envelope, as getting tangled in the dotted lines that connect the points on the two lines, that would mean that it would affect an area smaller than its own size on beta—a vastly larger area on alpha.

"So when a ship returns to alpha, it 'twangs' those connecting lines, setting up a sort of shock in our universe covering a volume of space nearly a parsec in diameter. It makes a sort of 'bong' sound on your T.V. set. Naturally, this effect occurs simultaneously over the whole volume of space affected. As a result, when an invader arrives, using inter-planar ships, we know instantaneously he is in the vicinity. Unfortunately, his sudden appearance and the ease with which he can disappear makes it impossible, even with this knowledge, to make adequate preparations to receive him. Even if he is in serious trouble, he has gone again long before we can detect the bong."

"Well, dear," said Anne.

"As usual, I'm sure you have made me understand perfectly. This time you did so well that I may still remember what stitching is by tomorrow. If the Oracle means anything at all by his statement, I suppose it means that we can use stitching to help defend ourselves, just as the invaders are using it to attack us. But the whole thing sounds completely silly to me. The Oracle, I mean."

Anne Bristol stood up, put her hands on her shapely hips and shook her head at her husband. "Honestly," she said, "you men are all alike. Paying so much attention to a toy you built yourself, and only last week you made fun of my going to a fortune teller. And the fuss you made about the ten dollars when you know it was worth every cent of it. She really told me the most amazing things. If you'd only let me tell you some of...."

"Darling!" interrupted John with the hopeless patience of a harassed husband. "It isn't the same thing at all. Buster isn't a fortune teller or the ghost of somebody's great aunt wobbling tables and blowing through horns. And Buster isn't just a toy, either. It is a very elaborate calculating machine designed to think logically when fed a vast mass of data. Unfortunately, it has a sense of humor and a sense of responsibility."

"Well, if you're going to believe that machine, I have an idea." Anne smiled sweetly. "You know," she said, "that my dear father always said that the best defense is a good offense. Why don't we just find the invaders and wipe them out before they are able to do any real harm to us? Stitching our way to their planets in our spaceships, of course."

Bristol shook his head. "Your idea may be sound, even if it is a little bloodthirsty coming from someone who won't even let me set a mouse-trap, but it won't work. First, we don't know where their home planets are and second, they have more ships than we do. It might be made to work, but only if we could get enough time. And speaking of time, I've got to meet with the Council as soon as we finish eating. Is dinner ready?"

After a leisurely meal and a hurried trip across town, John Bristol found himself facing the other members of Earth's Council at the conference table.

"I have been able to get an answer from the computer," he told them without preamble. "It's of the ambiguous type we have come to expect. I hope you can get something useful out of it; so far it hasn't made much sense to me. It's an old proverb. Its advice is undoubtedly sound, as a generality, if we could think of a way of using it."

The President of the Council raised his long, lean-fingered hand in a quick gesture. "John," he said, "stop this stalling. Just what did the Oracle say?"

"It said, 'A Stitch in Time Saves Nine.'"

"Is that all?"

"Yes, sir. According to the calculator, that gives us the best opportunity to save ourselves from the invaders."

The President absently stroked the neat, somewhat scanty iron-gray hair that formed into a triangle above his high forehead and rubbed the bare scalp on each side of the peak vigorously and unconsciously with his knuckles. "In that case," he said at last, "I suppose that we must examine the statement for hidden meanings. The proverb, of course, implies that rapid action, before a trouble has become great, is more economical than the increased effort required after trouble has grown large. Since our troubles have already grown large, that warning is scarcely of value to us now."

The War Secretary, who had grown plump and purple during a quarter of a century as a member of the Council, inclined his head ponderously toward the President. "Perhaps, Michael, the Oracle means to tell us that there is a simple solution which, if applied quickly, will make our present difficulty with the invaders a small one."

The President pursed his thin lips. "That's possible, Bill. And if it is true, then the words of the proverb should, as a secondary meaning, imply a course of action."

The Vice President banged his hands on the table and leaped to his feet, shaking with rage. "Why should we believe that this mountebank is capable of a solution?" he shouted in his stevedore's voice. "Bristol pleads until we give him enough millions of the taxpayers' dollars to make Bim Gump look like a pauper and uses the money to build a palace filled with junk that he calls Buster! He tells us that this machinery of his is smarter than we are and will tell us what we ought to do. And what happened after we gave him all the money he demanded—more than he said he needed, at first—and asked him to show something for all this money? I'll tell you what happened. His gadget gets real coy and answers in riddles. If we just had brains enough, they'd explain what we wanted to know. What kind of fools does this Bristol take us for? Neither this man nor his ridiculous machine has an answer any more than I have. We've obviously been taken in by a charlatan!"

Bristol, his fists clenched, spoke hotly. "Sir, that is the stupidest, the most...."

"Now just a minute, John," interrupted the President. "Let me answer Vice President Collins for you. He's a little excited by this whole business, but then, these are trying times." He turned toward the glowering bulk of the Vice President. "Ralph," he said, "you should know that every step in the design, the construction and the—er—the education of the Oracle was taken under the close watch of a Board of eminent scientists, all of whom agree that the computer is a masterpiece—that it is a great milestone in Man's efforts to increase his knowledge. The Oracle has undoubtedly found a genuine solution to the question Bristol asked it. Our task must be to determine what that solution is."

"I can't entirely agree with that," said the Secretary for Extra-Terrestrial Affairs in a thin half-whisper. "I think we should depend on our own intelligence and skill to save ourselves. I've watched events come and go on this planet of ours for a long time—a very long time—and I feel as I have always felt that men can make the world a Paradise for themselves or they can destroy themselves, but that nothing else but they themselves can do it. We men must save ourselves. And there are still things that we can do." He shrugged his ancient, shawl-covered shoulders. "For example, we could disperse colonies so widely that it would become impossible for the invaders to destroy all of them."

"I'm afraid that's no good, George," answered the War Secretary respectfully. "If the Solar System is destroyed, any remaining colonies will be too weak to maintain themselves for long. We must defend this system successfully, or we are lost."

"Then that brings us back to the Oracle's proverb." The President thought for a moment. "Stitching obviously refers to inter-planar travel. How can that help us?"