All along the base of the Wall, shrubs and vines crept upward in thick, tangled clumps, as if the presence of the Wall made the soil at its base more fertile than elsewhere on the hills. Blade and Twana started north, while Blade looked for a vine or tree strong enough and tall enough to carry him to the top of the Wall. Twana kept an eye out for the Watchers. She was pale and moved with little jerky steps, as though she expected the Watchers to rise out of the ground in front of her at any moment. But she was also alert and kept up well.

In an hour they'd left the Shoba's men out of sight in the haze and mist to the south. Twana was beginning to mutter, «Where are the Watchers?» Blade would have liked an answer to the same question. Here they are, marching steadily along the very base of the Wall, without the faintest sign that the Watchers even existed. If the legends were entirely true, they should have been dead by now.

Somebody else had risked the Watchers, a long time in the past. Blade saw a place where at least a ton of gunpowder must have been set off against the base of the Wall. The rock was split and shattered, and a blackened hole revealed several feet of the Wall's foundations. The Wall itself showed a faint discoloration and some barely visible pitting, but otherwise the explosion had left it completely unaffected.

Another hour's walking brought Blade and Twana to a stretch of Wall three hundred yards long and completely overgrown with massive vines from ground level all the way to the top. A six-year-old child could have scrambled up those vines, let alone a trained athlete like Blade, who had climbed the face of the Eiger.

He went up carefully though. He weighted a good deal more than any six-year-old child. If the vines did break under him, he might be dropped forty or fifty feet onto hard rock.

A broken leg here and now could be a good deal more fatal than the Watchers.

Foot by foot, Blade clambered upward. In places his fingers pushed through the tangle of vines and touched the Wall itself. When he did that, he could feel a faint, irregular vibration within the blue-gray material. It was like putting his fingers on the head of an enormous drum being gently tapped by an invisible drummer. Once he was able to put his ear against the Wall and hear a distant humming that came and went in irregular pulses. The Wall was not as dead as it seemed, or perhaps even as solid.

The last few feet were particularly tricky. The vines were growing thinner, the twice strands broke as Blade gripped them. Both times he hung there with a death clutch on the broken strands, barely breathing, toes curling for a better foothold.

At last there was no more Wall to climb, only a flat surface like a blue-gray tabletop stretching out of sight. The golden shimmering in the air above the Wall was clearly visible now. It seemed to start three or four feet above the top and then curve upward and away toward the inner side of the Wall. It was soundless, odorless, unchanging, and totally unlike anything Blade had ever seen or imagined. It reminded him that, as he explored the Wall, he might be in the position of a caveman trying to examine and understand a jet bomber — or an atomic reactor.

Blade scrambled out onto the top of the Wall. On hands and knees he crawled forward. He held his sword in one hand, probing the featureless surface ahead of him as he moved.

He covered forty feet, and then suddenly he could no longer see. It was as if he'd stuck his head into a black sack. He drew back, startled, and vision instantly returned. He looked ahead, at both the Wall and the air above it. High above he caught hints of the golden shimmering. Directly in front of him, he could see nothing at all except the top of the Wall. He crawled forward-and again the world vanished around him.

He tried three more times, until his head was beginning to spin with the repeated coming and going of his vision. By that time he realized what had to be wrong. The Wall was generating some sort of field that completely deprived him of vision. That field started at a point only a yard or so in front of him and continued until…

That was a question he'd have to answer, sooner or later. Not now though. Not when he had Twana to get back home and the Shoba's men were still close enough to take advantage of any mistakes he might make. He crawled back to the edge of the Wall and stood up slowly. As his head rose into the golden shimmering, he had a moment's sensation of being jabbed with thousands of tiny blunt needles. Then the sensation faded. Whatever the shimmering meant, it did not appear to be dangerous.

Blade tied a loop in the end of the rope and threw the loop down to Twana. She caught it and drew it around her body. Then Blade began to back slowly away from the edge of the Wall, pulling Twana up as he did.

He was also keeping watch on either side of him, along the top of the Wall. It rose and fell in long, slow curves, like waves far out at sea. It was totally bare. In a few places it looked as though it had even been scraped or sandblasted clean.

That thought reminded Blade of the Watchers. He was beginning to wonder if they had ever existed, except in the legends of the village people. Here he was on top of the Wall, and he still seemed to be completely invisible to whomever or whatever might be on guard. He was also perfectly happy with this situation.

As Twana's head appeared over the edge, Blade caught another flash of the sun on polished metal. This one was far to the south and came and went so quickly that he wasn't completely sure he hadn't imagined it. He reached down and helped Twana up onto the level surface. She lay gasping for a moment, then rose to her knees and reached for her water bottle. As she drank, Blade again scanned the top of the Wall in both directions, as far as he could see.

Whatever had made the flash was now invisible again. A Watcher? A large metal machine such as Twana had described could make the kind of flashes he'd seen when the sun caught it at the right angle. If the Watchers existed, that is-and if they existed, then where were they?

Blade and Twana moved swiftly north along the smooth top of the Wall. They went barefoot to reduce noise and leave no visible traces. They kept just far enough away from the edge of the Wall to be invisible from the ground without wandering into the blindness field. If the Watchers no longer mounted a reliable guard on the Wall, the Shoba's men might also discover this. Then they might be willing to climb the hills, and the chase would be on again.

Blade decided that he and Twana would stay up on the Wall for two days, moving as far as they could in that time. That should leave the Shoba's men far behind. With the enemy off their trail, they could return directly to Hores. Blade was no longer quite sure what he'd be doing after that. This Dimension was developing more than the usual quota of mysteries. The Wall seemed to be only a starting point.

They'd been walking for two hours when Blade saw metal flash again, three times in five minutes. The flashes were a good ten miles away, but this time they were to the north. He stopped and desperately strained his eyes to see what might be waiting for them but saw nothing-not even a hint of movement.

After a few minutes they moved on. Blade no longer felt quite so willing to believe that the Watchers were a myth. It occurred to him that they might be playing games with him, like a cat with a mouse, waiting for their chosen moment to strike.

They walked along the Wall all through the rest of the morning and into the afternoon. Every hour or so Blade went down on his belly and crept to the edge of the Wall to examine the plain below. The Shoba's men were nowhere in sight.

Blade decided that, if their pursuers were still out of sight the next morning, he and Twana would climb down from the Wall and take to the ground again. It would be a gamble, but he was beginning to feel it would be less of a gamble than staying on the Wall. Blade had almost a wild animal's instinct for detecting danger, and that instinct was now sending him a clear message. They told him that the Wall was protected by Watchers or by something that was waiting, invisible for the moment, but able to turn deadly dangerous in the blink of an eye.