Moving silently took concentration. The air seemed to coil up into her nose, filling her lungs with thick musk. They reached the barrier just as Tananareve was starting to feel woozy. Her arm ached. Lau Pin thought the tall, slick wall was slightly lower here, due to some sagging. A huge tree had fallen into it from the other side, pulling it down somewhat. It was uncomfortably close to a spidow corridor, too.

Quickly they deployed their loops of spidow string. Lau Pin and Abduss began linking the coils, fusing them together with quick bursts of laser light, raising a stench like burnt milk. They had practiced this craft and now could seal the ends within seconds, playing the beams along the ends until they bubbled.

Tananareve took her position along the barrier, as they had drilled. The wall was transparent and slick, probably to keep animals from climbing it. Easily a hundred meters high, too. She looked through the wall at the jungle beyond. The wall was like ancient glass, with whorls and ripples that toyed with the view. She realized that that must be exactly what it was—glass so old, it had warped through its slow slide downward, for glass was a fluid. These must be some sort of standard wall, used for keeping animals within their range. But not, apparently, smart animals.

Working quickly, Lau Pin and Abduss fused the end of the coiled filaments to a chunk of wood. Lau Pin had cut and sized these days before. He had proved handy at woodcraft and more. The ropy, rubbery vines nearby he had built into a curious kind of slingshot—taut vines, a cantilevered flinging pouch, artfully angled struts. He and the others cocked his array back, grunting. The men had practiced this and seemed confident it would work. A tanned and stretched leaf held the wood block payload, the ropes straining at it. They all took their positions as Lau Pin counted down.

Tananareve had to admire how Lau Pin had made this with Abduss. The entire taut machine was like something from the Middle Ages—and they had built it from scratch.

“Fire!” Lau Pin couldn’t resist whispering.

The energy stored in the stretched vines sent Abduss’s payload shooting upward, arcing high. It cleared the barrier lip and started down on the other side. In 0.1 g, a slingshot had ten times the range it would have on Earth. That simple physics had led to many comic miscalculations as they learned to walk and work here on the terrace, but now the difference paid off. The soaring block pulled the spidow thread smoothly out of the coils. The block struck the ground with a thump she could barely hear.

“Over!” Lau Pin called.

Beth scrambled up the threads, hand over hand. The pale fibrous stuff was strong and slightly sticky, just enough to get a hold. She went up fast in the low g.

But something moved behind them.

Tananareve turned and saw two spidows moving off the threads about a hundred meters away, in the channel of their threads. How did they know? she had enough time to think. Vibrations? The stench?

Then the spidows came at them.

Abduss turned and fired his laser at both the approaching shapes. The spidows kept coming. He hit one in the four eyestalks and it bucked back, showing a mouth of converging black teeth like pincers. They made not a sound, but the wounded one reared up, as if to frighten them with its size. At that moment, Tananareve fired her laser into its belly. The thing came down with a crash. It didn’t move.

But its partner did not slow. It brushed aside big trees as if they were saplings, ripping some out by their roots. Abduss held his ground and Tananareve saw the others were going up the thread, hand over hand. She fired again but the second spidow seemed invulnerable. It took the bolts without a pause. She heard from it a high, thin shrill.

“Go!” Abduss called to her. “Up!”

She fired one last time at the spidow. It was moving slower but was only twenty meters away. Tananareve tucked her laser into her belt and leaped for the thread. Her arm gave a sharp spike of pain. She favored that arm and went up, hand over hand, kicking off against the wall to try to get more momentum.

The spidows could climb the thread, of course. She had not thought of that before. They had worried about the Serfs and Memor, but the spidows were the present threat.

She was halfway up when she heard a scream. She could not help looking down.

Abduss was under the spidow, and with a gurgle the screaming stopped. But the spidow did not linger. It tilted up and with its arms it grabbed at the thread. The arms were long and sinewy and moving so fast, they were a blur.

It launched itself upward. Behind it, Abduss looked like a tissue someone had crumpled up after a nosebleed.

It was coming for her. The thin, cutting shrill was loud now.

She pulled furiously at the thread, kicked with her toes. She could hear the huge thing sucking air in and out now with long, windy breaths.

The thread jerked with the weight behind her. She looked up and there was Lau Pin, aiming down from the top of the wall. A crisp sizzle raked the air near her head. Dazzles flashed in her eyes, evaporated away. Another sizzle. Her breath rasped and she ignored the snap in her shoulder.

Lau Pin held out a hand and when she took it he lifted her bodily free of the thread. With one hand he brought her to the lip and she angled herself over, rolling to stay out of his way.

He said, “No way I—” Another sharp sizzle near her hand. The thread went limp in her hand.

She canted over the lip, gasping. Her hands grabbed it and she tumbled over, facing the wall. The brown and gray spidow mass was just below her. She thumped against the wall, mashing her nose. Blood drooled down her face.

She looked around. Lau Pin was falling away below her. He had laser-cut the thread and—the spidow was falling. It went straight down, getting smaller in slow motion. No sound now.

She hung there, holding on, watching it thud below. And flatten down, graceful and quick as a cat. Scrabbling legs, a long low mournful sound. It got larger then. It had absorbed the fall in its legs and now—it leaped for her.

Missed. Fell back. Would try again.

She let go with one hand, the weak arm, and turned her back to the wall, clunking into it.

Below were faces. The thread had fallen into coils below her and the others looked up at her. A long fall, over a hundred meters. They waved their arms and their mouths moved, but with the pulse pounding in her ears she could not make out what they said.

The spidow was coming. Maybe it had a way of clinging to the wall. She did not wait to find out.

A treetop beckoned about fifty meters below. It looked leafy and thick, with few branches showing. In this low g—no, not the time to do a calculation.

She gathered her feet and pushed off—toward the treetop.

She tumbled and tried to come down on her boots. When she hit, the leaves lashed at her. Branches snapped against her boots, arms; one caught her smack in the face. She hit a large limb, pain lancing into her ribs. It hurt badly as she tumbled headfirst through—into clear air—and managed to get her boots under her.

She hit hard. Collapsed. Rolled away, trying to get a look up at the spidow.

It came through the tree after her. Slamming through, snapping even the big branches, showering leaves and limbs down. It had punched its way through and crashed to the ground right beside her.

Beth shot it through the enormous, many-eyed head. It jerked, gave a high, thin wail—and went still.

When Tananareve looked through the wall, she could see Abduss, as still as the spidow.

PART V

Nothing in biology makes sense except in the light of evolution.

—T HEODOSIUS D OBZHANSKY