The buzzer of their radiophone was sounding, but so intent were they on this phenomenon they were facing, they paid it no heed. Their eyes were alight, their lips in firm straight lines of resolve, as they dived down upon the invisible obstruction—whatever it was—from whose surface the telltale updraft came.

It was Eyer who made the suggestion:

"Let's measure it to see what its plane extent is."

"How?" asked Jeter.

"Measure it by following the wind disturbance. We travel in one direction until we lose it. There is one extremity. In a few minutes we can discover exactly how big the thing is. What do you think it is?"

Jeter shook his head. There was no way of telling.

Jeter nodded agreement to Eyer. Then he spoke into the radiophone, telling Hadley what they had found, to which he could give no name.

"The world awaits in fear and trembling what you will have to report, Jeter," said Hadley. "What if you become unable to report, as Kress did?"

"Don't worry. We will or we won't. If we succeed we'll be back. If we fail, send up the other.... No, perhaps you hadn't better send up the new planes. But I think Eyer and I have a chance to discover the nature of this strange—whatever-it-is. If you can't contact us, delay twenty-four hours before doing anything. I—well, I scarcely know what to tell you to do. We'll just be shooting in the dark until we know what we're in for. You'll have to contain yourself in patience. What did you want with me?"

"Only to tell you of another strange news dispatch. It gives no details. It merely tells of strange activity around Lake Baikal, beyond the Gobi Desert. Queer noises at night, mysterious cordons of Eurasians to keep all investigators back, strange losses of livestock, foodstuffs...."

Jeter severed connection. There was little need to listen further to something which he couldn't explain yet, in any case.

Eyer, at the controls, banked the plane at right angles and flew on. In shortly less than a minute he banked again.

In five minutes he turned to Jeter with a queer expression on his face.

"Well," he said, "what's to do about it? What is it? It seems to be some solid substance approximately a quarter mile square. But it can't be true! A solid substance just hanging in the air at ninety thousand feet! It's beyond all imagining!"

"What man can imagine, man can do," replied Jeter. "A great newspaper editor said that, and we're going to discover now just how true it is."

"What's our next move?"

For a long time the partners, stared into each other's eyes. Each knew exactly what the other thought, exactly what he would propose as a course of action. Jeter heaved a sigh and nodded his head.

"We're as much in the power of the enemy here as we would be there, or anywhere else. We can't discover anything from here. Set the wheels down!"

"We can't tell anything about the condition of the surface of that stuff. We may crack up."

Jeter had to grin.

"Sounds strange, cracking up at ninety thousand feet, doesn't it? Well, hoist your helicopter vanes and drift down as straight as you can—but be sure and keep your motor idling."

Again they exchanged long looks.

"O.K.," said Eyer, as quietly as he would have answered the same order at Roosevelt Field. "Here we go!"

He pressed a button and the helicopters, set into the surface of the single sturdy wing, snapped up their shafts and began to spin, effectually slowing the forward motion of the plane. Eyer fish-tailed her with his rudder to help cut down speed.

"We can't see the surface of the thing at all, Lucian," said Eyer. "I'll simply have to feel for it."

"Well, you've done that before, too. We can manage all right."

Down they dropped. The updraft was now a cushion directly under them. And then their wheels struck something solid. The plane moved forward a few feet—with a strange sickening motion. It was as though the surface of this substance were globular. First one wheel rose, then dipped as the other rose. The plane came to rest on fairly even keel, and the partners, while the motor idled, stared at each other.

"Well?" said Eyer, a trace of a grin on his face.

"If it'll hold the plane it will hold us. Let's slide into our stratosphere suits and climb out. We have to get close to this thing to see what it is."

"Parachutes?" said Eyer.

Jeter nodded.

"It would simplify matters if the thing happened to tilt over and spill us off, I think," said Jeter, matching Eyer's grin with one of his own. "I can't think with any degree of equanimity of plunging ninety thousand feet without a parachute."

"I'm not sure I'd care for it with one," said Eyer.

They were soon in the tight-fitting suits which were customarily used by fliers who climbed above the air levels at which it was impossible for a human being to breathe without a supply of oxygen in a container. Their suits were sealed against cold. Set in their backs were oxygen tanks capable of holding enough oxygen for several hours. Over all this they fastened their parachutes.

Then, using a series of doors in order to conserve the warmth and oxygen inside their cabin, they let themselves out, closing each successive door behind them, until at last they faced the last door—and the grim unknown. They glanced at each other briefly, and Jeter's hand went forth to grasp the mechanism of the last door. Eyer stood at his side. Their eyes met. The door swung open.

They stepped down. The surface of this stratosphere substance was slippery smooth. Now that they stood on its surface they could sense something of its profile. Movement in any direction suggested walking on a huge ball. The queer thing was that they could feel but could not see. It was like walking on air. Their plane appeared to be suspended in midair.

For a moment Jeter had an overpowering desire to grab Eyer, jerk him back to the plane, and take off at top speed. But they couldn't do that, not when the world depended upon them. Had Kress encountered this thing? Perhaps. How must he have felt? He had been alone. These two were moral support for each other. But both were acutely remembering how Kress had come back.

And his plane? They'd perhaps discover what had happened to that too.

Eyer suddenly slipped and fell, as though he had been walking on a carpet which had been jerked from under his feet. From his almost prone position he looked up at Jeter. Jeter dropped to his knees beside him. Their covered hands played over the surface of their discovery, to find it smooth as glass. As though with one thought they placed their heads against it, right ears down, to listen. But the whole vast field seemed to be dead, lifeless. And yet—a solid it was, floating here in space—or just hanging. It seemed to be utterly motionless.

"There should be a way of discovering what this is, and why, and how it is controlled if an intelligence is behind it." Jeter spelled out the words in the sign language they had both learned as boys.

Eyer nodded.

They walked more warily when they had, traveling slowly and hesitantly, gone more than a hundred feet from their plane. They kept it in sight by constantly turning to look back. It was now several feet above them. No telling what might happen to them at any moment, and the plane was an avenue of escape.

They didn't wish to take a chance on stepping off into the stratosphere—and eternity.

"It's like an iceberg of space," said the fingers of Jeter. "But let's go back and look it over to the other side of the plane. We have to keep the plane in sight and work from it as a base. And say, what sort of sensations have you had about this surface we're standing on?"

Jeter could see Eyer's shudder as he asked the question. Slowly the fingers of his partner spelled out the answer.

"I've a feeling of eyes boring into my back. I sense that the substance under us is malignant, inimical. I have the same feeling with every step I take, as though the unseen surface were endowed with arms capable of reaching out and grabbing me."

"I feel it, too," said Jeter's fingers. "But I'm not afraid of fingers in the usual sense. I don't think of hands strangling us, or ripping us to shreds, but of questing—well, call them tentacles, which may clasp us with gentleness even, and absorb us, and annihilate us!"

Now the two faced each other squarely. Now they did not try to hide that their fear was an abysmal feeling, horrible and devastating.

"Let's get back to the plane and take off. We haven't a chance."

They clasped hands again and started running back, their plane their goal. Before they reached it they would change their minds, for they were not ordinarily lacking in courage—but so long as they ran both had the feeling of being pursued by malignant entities which were always just a step behind, but gaining.

They slipped on the smooth surface face and fell sprawling. Each felt, when he fell, that he must rise at once, with all his speed, lest something grasp him and hold him down forever. It was a horrible trapped feeling, and yet....

They had but to look at each other to see that they were free. Nothing gripped their feet to hold them back. Of course the way was slippery, but no more so than an icy surface which one essays in ordinary shoes. What then caused their fear?

The plane, so plainly visible there ahead and above, was like a haven of refuge to them. They panted inside their helmets and their breath misted the glass of their masks. But they stumbled on, making the best speed they could under the circumstances.

Perhaps if they took, off, and regained their courage, returned to normal in surroundings they knew and understood, they could come back and try again, after having heard each other's voices. The silence, the sign manual, the odd, awesome sensations, all combined to rob them of courage. They must get it back if they were to succeed. And they had been away from the plane for almost an hour. Hadley would be waiting for some news.

The plane was twenty yards away—and almost at the same time Eyer and Jeter saw something queer about it. At first it was hard to say just what it was.

They rushed on. They were within ten yards of the plane when a wail of anguish was born—and died—in two soundproof helmets. There was no questioning the fact that the plane had settled into the surface of the field.

The plane was invisible below the tops of the landing wheels, as though the plane were sinking into invisibility, slowly dissolving from the bottom.

"Understand?" Jeter's fingers almost shouted. "Understand why we felt the desire to keep moving? This field is alive, Eyer, and if we stand still it will swallow us just as it is swallowing our plane! Let's get in fast; maybe we can still pull free from the stuff and take off."

They were racing against time and in the heart of each was the feeling that whatever they did, their efforts would be hopeless. Still, the spinning propeller of their plane gave them strength to hope.

They went through the succession of doors as rapidly as they dared. Once in the comfort of their cabin they doffed their stratosphere suits with all possible speed. Jeter was the first free. He jumped to the controls and speeded up the motor. In a matter of seconds it was revving up to a speed which, had it been free, would have pulled the plane along at seven hundred miles an hour at the height at which they were.

But the plane did not move!

Jeter slowed the motor, then started racing it fast, trying to jerk the fuselage free of the imbedded wheels, but they would not be released. Both men realized that the wheels had sunk from sight while they had been delayed coming through the succession of doors—that the plane had sunk until the invisible surface gripped the floor of the fuselage.

Perspiration beaded the faces of both men. Eyer managed a ghastly grin. Jeter's brow was furrowed with frantic thought as he tried to imagine a way out.

"If we could somehow cut our landing gear free," began Jeter, "but—"

"But it's too late, Lucian," said Eyer quietly. "Look at the window."

They both looked.

Countless fingers of shadowy gray substance were undulating up the surface of the window, like pale angleworms or white serpents of many sizes, trying to climb up a pane of glass.

"Well," said Jeter, "here we are! You see? Outside we can see nothing. Inside we begin to see a little, and what good will it do us?"

Eyer grinned. It was as though he lighted a cigarette and nonchalantly blew smoke rings at the ceiling, save that they dared not use up any of their precious oxygen by smoking.

Their fear had left them utterly when it would have been natural for them to be stunned by it.