A mad enterprise indeed--a ghost and a zombie, going to seek out a foe whose numbers and whose might grew ever more apparent. The tunnel opening here was clear evidence of engineering resources and skill far beyond that of any of the machine races Dworn knew.

Its discovery was no help to them, since it was far too small to admit the spider.

"Go on!" Dworn ordered doggedly. "At least we know now that _their_ dwelling can't be far!"

Qanya glanced briefly sidelong at him, then moved the levers, and the spider rocked upright once more and began to climb.

The sun was low, and the shadows of rocks and dunes in the valley behind them were pointing long blue fingers eastward, when the machine staggered up the last precipitous ascent and stood on level ground at the summit.

Dworn took a deep breath and looked ahead, looked for the first time in his life upon the unknown land beyond the Barrier.

At first glance, it differed little from any of the desert country where he had lived all his life. The ground shelved gradually away from the rocky rim on which they stood; far off, against the darkening eastern sky, blue mountains rose murkily, but between here and the ranges lay a vast shallow depression, an arid sink floored with wind-rippled sand.

Perhaps it had been a lake-bed once, before natural or unnatural cataclysms, and the millennial drying-up of all this country, had emptied it of water. Or perhaps--as its circular form suggested--it was one of those other, mysterious depressions which were scattered irregularly across the face of the earth where no lakes had ever been; those, legend said, were scars left by the ancients' wars.

The rich light of the declining sun fell at a shallow angle into the miles-wide bowl and brought out with startling clarity the maze of wheel-tracks, crossing and criss-crossing, which covered its sandy expanse and testified to a fever of recent machine activity there. The light gleamed, too, here and there, upon scurrying metallic shapes, that raced by ones and twos or in trickling columns to and from the center of the bowl, where--

Dworn strained his eyes and his capacity for belief in an effort to make sense of the structures there, miles away. He was not very successful, for the scene was too unlike anything he had ever looked on before.

There were certain races which built stationary dwellings--Dworn knew of the scale-makers who lived, in colonies sometimes of considerable size, beneath individual armored, anch.o.r.ed domes sunk into the face of some impregnable rock; he knew of the sand devils with their pits, and now he had seen also how the spider people nested. But the huge buildings that loomed yonder, lowering and windowless, and the winged things cl.u.s.tering thick on the ground about them, were such as he had never seen in his nomadic life.

Atop a slender tower that spired above the squat structures he could make out something which turned and turned, something like a broad net of lacy wires, revolving steadily from east to west, from north to south. Strange, too, the smooth-surfaced ways that radiated outward in four directions, like an immense cross, broad paved roads that came to abrupt dead ends a mile or more from the central buildings.... After a moment, though, he guessed that those were runways for the aircraft which flew from this place.

The unknown builders were obviously a mighty people, a people who had perfected their peculiar form of organization on a gigantic scale. And a people who acted and thought strangely; for their behavior, as Dworn had observed it, suggested a chilly-blooded and fanatic discipline, a regimentation which he found monstrous and repellent.

Dworn turned questioning eyes on Qanya.

"I don't know what they are," she answered his unspoken query in a voice that faltered. "I remember this valley. But a few months ago it was uninhabited. All this has been built since then."

Dworn hesitated. He was seeing very clearly now just how hopeless this mad expedition was. Nevertheless, he had sworn vengeance, and he could at least perish with honor.

But--Seeing the fear in Qanya's face, it came to him sharply that, after all, she had no part in his blood feud. She had served him well by bringing him this far. The vague plans he had had, of using the spider-machine for an attack on the enemy, stood revealed as rankest folly. Big and powerful as the spider was by ordinary standards, against such as those it could accomplish little more than a man with his bare hands.

Which was what Dworn would be--He stifled further reflection, said crisply: "You can go now. I'll remain here; I have a duty to perform.

But you can return--go make your peace with your people, or whatever you like."

Qanya's black eyes met his squarely. "I won't," she said.

"Now see here--" Dworn began, and broke off, thunderstruck.

"B-but," he gulped, "you _can't_ disobey me. The drug, the spider poison--"

"Doesn't work on a born spider. I must have neglected to mention that, naturally, _we're_ all immunized against it." She smiled with a flash of those sharp white teeth.

"Then--then--" Dworn stumbled, feeling his preconceptions tossed helter-skelter. "Then you must have come with me--of your own free will!"

"At first," murmured Qanya, "I knew you'd never trust me unless I pretended ... and I was curious, too, to see how it was to be the one that obeyed. And then ... well, you'd have known, if you'd ever seen how the drug really works. You should have realized, anyway, when I laughed at you.... But you do so love to be masterful don't you?"

For a moment, Dworn's chief emotion was one of quick rage at the revelation of how thoroughly she'd deceived him. Then the anger subsided and left him feeling merely foolish, as he saw that she'd merely let him deceive himself. And, finally--as it came home to him that this girl had followed him of her own choice into exile and great danger--a new and quite unaccustomed feeling flooded in on him, a queer sense of humility.

"I'm sorry," he said confusedly. "I didn't--I don't--understand."

She breathed in a barely audible voice, "You said I was beautiful....

And _you_ hadn't the drug."

From far away, from around the vast, mysterious buildings, came mournful hooting sounds, a sighing and a sobbing as of some mythical monster in torment.

Dworn was rudely recalled to realization of where they were--and of the fact that, as the spider-machine stood poised here on the cliff-edge, it would be starkly visible from over there, seen against the setting sun.

He gave up trying to unsnarl the tangle of his own feelings. He said hurriedly, "But you should go back. There's no time--I _have_ to go on.

But there's no reason you should die."

Qanya's face was drawn and determined. "No," she said flatly.

"I don't know what you're talking about. But I won't leave you now...."

The distant sighing rose to a whining roar.

"Quick!" cried Dworn in desperation. "Find cover. I think we've been seen!"

The girl reached for the controls and the spider's engine raced up. But it was already late. Off yonder, along that one of the radiating runways that stretched toward them, something was moving, racing swiftly and more swiftly outward with its long shadow following it.

All at once the moving thing left its shadow behind, and Dworn recognized it for an aircraft taking off.

Then he had to s.n.a.t.c.h for a handhold as the spider-machine lunged into a dead run. At full speed on the level ground, it could make good time; the ground outside skimmed past at fifty or sixty miles an hour.

Qanya had spied some rocky outcroppings, which might furnish a modic.u.m of shelter, about a mile away and some distance from the brink of the cliffs, and she was heading for them. But the terrain nearer at hand was implacably flat--and the enemy was airborne, a vicious winged shape growing at terrifying speed. Its whistling roar swelled and grew deafening.

Qanya shouted something inaudible and pointed. Dworn understood, and, holding on for dear life in the pitching cabin, clawed his way within reach of the fire-controls. Wrestling with the unfamiliar mechanism, he fought to train the spider's guns on the hurtling attacker.

Puffs of smoke bloomed high in air--but any hit on such a fast-moving target, from so unstable a platform, would have been a miracle. The enemy screeched overhead, and an instant later flame and thunder erupted all around the running spider. The machine stumbled and for a moment seemed going down, but it righted itself and staggered on.

Dworn shook his ringing head and saw the flier banking steeply half a mile away, while a second and a third were climbing against the sky, gaining alt.i.tude to dive.

They couldn't last another thirty seconds, couldn't even hope to reach the doubtful cover of the rocks.... Up ahead, two hundred yards, was a low mound, only a few feet high, the only nearby elevation of any sort.

And it was plainly artificial, though wind-piled sand had softened its outlines; others like it were scattered around the periphery of the great sink, and Dworn guessed their nature as he saw a column of the aluminum crawlers beginning to emerge from the side of the one just ahead. It must be the other end of a tunnel such as they had discovered among the cliffs....

He nudged Qanya urgently, shouted, "Head for that!"

She gave him a fleeting, wide-eyed look. The mound's low swell could furnish no shelter for the towering spider, and the tunnel mouth was of course much too small to enter. But she veered without slackening speed in the direction indicated.

Dworn abandoned the useless guns. The mound, with a gleaming line of crawlers still parading out of it, swept closer; and at the same time the desert echoed back the screaming onrush of the two new attackers.