Behind the humans stood Mandelbrot, the only one of the four robots on board present in the control room. He was an old-model robot of steel and plastic construction-save for his more recently repaired right arm-and he wore no clothing over his angular body plating, nor did his visual sensors or speaker grille convey a readable expression.

Derec, his eyes drifting from the viewscreen to his companions and back, was the first to voice the question all of them were thinking: “You’re sure this is the right planet?”

Wolruf, swiveling slightly around in the pilot’s chair, nodded her toothsome head. “Positive.”

“Then what happened to it?” Ariel asked.

“That’s ‘arder to say.” Wolruf pushed a button to lock the viewscreen picture in place, then moved a slide control upward, increasing the screen’s magnification until the planet’s mottled surface began to show detail. Where they had expected to see the sharp angles of buildings and streets, they saw the tufted tops of trees instead. Narrow pathways wound among the trees, and as Wolruf increased the magnification still further they saw that the paths occasionally joined at landmarks ranging from boulders to dead tree stumps to natural caves. There were no buildings in evidence at all.

The angle of view changed steadily as the ship continued to move in orbit, until they were looking out rather than down over a sea of treetops. The picture grew less and less sharp as the angle changed, and after a moment Derec realized it was because the lower their view angle got, the more atmosphere they had to look through.

“Try another view,” he said to Wolruf, and the golden-furred alien backed off the magnification and released the hold. The camera tracked forward again and the picture became a blur of motion until they once again looked directly downward from the ship.

A ragged boundary line between the green forest and a lighter green patch of something else caught Derec ‘ s attention. “There,” he said. “Zoom in on that.”

When Wolruf did so, they could see a vast meadow of waving grass. It wasn’t like a farmer’s field, all of one type and all the same height, but rather a patchwork of various species, some tall, some short, with bushes and the occasional tree scattered among them. Again there were paths, though fewer than in the forest, and again the scene lacked any sign of human habitation. There were inhabitants, though: small knots of four-legged animals grazing under the watchful eyes of circling hawks or eagles.

“How did they get there?” Dr. Avery demanded.

Derec glanced over at his father, opened his mouth to answer, then thought better of it. He turned back to Wolruf and said instead, “Let’s try another view.”

Wolruf provided it. This one showed a barren expanse of sand, punctuated sporadically by lone stands of cactus. Near the edge of the screen a single tree cast its shadow across a pool of water. A smallish four-legged animal of some sort lapped at the water, looking up frequently to check for predators.

“They really took it seriously,” Derec muttered, scratching his head in bemusement.

“Took what seriously?” Avery demanded. “This is your doing, isn’t it?”

Derec nodded. “I suppose it must be, though I certainly didn’t expect this.”

“What did you expect? What did you order them to do?”

Derec faltered for a starting point, said at last, “You remember our argument just before we left, when I wanted to use the animals Lucius had created as the starting point for a real biological ecosystem, but you had the hunter robots kill all of them instead? Well, when we boarded the ship, I told the computer to access my files on balanced ecosystems, and to…well…to make one based on what it found there.”

Avery visibly considered his response to that revelation. His fists clenched and unclenched, and the tendons in his neck worked as he swallowed. Mandelbrot took a step toward Derec, readying to protect his master should Avery decide to attack him physically.

Avery noticed the motion, scowled, and lashed out with a kick to the robot’s midsection instead. The hollow clang of shoe against metal echoed in the control room. Concurrent with the kick, Avery shouted, “Why do you always have to do this to me? Just when I think I’ve got something running smoothly, you go and throw sand in the works. Literally.” He waved at the screen, still showing desert, but at such a low angle now that the atmospheric disturbances between it and the ship made it shimmer as though they were actually standing in its midday heat.

Mandelbrot had rocked back with the kick, absorbing the blow so Avery wouldn’t hurt his foot, but that was his only move. Derec looked from his father to the robot and back again. In a way, Mandelbrot was Derec’s first real achievement in life. He had reconstructed the robot from parts, and in the years since then the robot had grown from a servant to a companion. Perhaps for that reason, Avery had mistreated the poor thing since the day they had met. Derec had been about to apologize for his mistake with the city, but now, in answer to Avery’s question, he said simply, “Maybe it’s a family trait.”

They stared at one another for long seconds, their anger weighing heavy in the room, before Ariel said in disgust, “Boys.” Dismissing them and their argument, she stepped around Derec to stand beside Wolruf’s chair, saying, “Can you find any sign of the city at all?”

“Not visually,” the alien admitted, “but we ‘ave other methods.” She spent a moment at the controls, during which the viewscreen image zoomed out again, blurred, shifted to false color imaging, and displayed what might have been a color-coded topographic map.

“Definitely getting neutrino activity,” she said. “So something’ s still using microfusion powerpacks. “

Derec relinquished the staring match in order to see the viewscreen better. “Where?” he asked.

“Everywhere,” Wolruf said. “Many sources, scattered allover the planet. Even more beneath the surface. “

“Has the city gone underground?” asked Ariel.

“We’ll see. “ Wolruf worked a few minutes longer at the controls, explaining as she went. “I’m trying penetration radar, looking for ‘ollow spots. And sure enough, there they are.” On the screen a shadowy picture showed the familiar rectangular forms of a city.

“What’s on the surface above them?” It was Avery, his tone almost civil.

Perhaps as a reward, or perhaps out of her own curiosity, Wolruf replaced the radar image with the visual once again and they found themselves looking down on a wide, flatbottomed river valley. The river that had carved it meandered lazily through stands of trees, past low bluffs covered with grass and bushes, and on without hindrance out of the viewscreen’ s reach. No remnant of the city that once covered the planet’s entire surface marred the now perfectly natural setting, and nothing visible in normal light indicated that below it lay anything but bedrock.

The sight of bare ground without city on it rekindled Avery’s ire. “And just how are we supposed to get inside?” he demanded.

Without looking up at him, Ariel said, “There must be access hatches or something. “

“And how do we find them?”

“By asking.” Mandelbrot paused for the half second or so it took for everyone to look at him, then added, “I am now in communication with the city’s central computer. It confirms Ariel ‘ s assertion: elevators to the surface have been provided in the new city plan. It can direct us to anyone of them we wish to use.”

Wolruf laughed the gurgling laugh of her kind. “What difference does it make? It’s all the same anyway.”

“All except the Compass Tower,” said Avery. He looked from Wolruf to Derec. “Provided it’s still there.”

“It is,” Mandelbrot replied. “The original city programming was inviolate in its case. It is the only building on the planet that remains above the surface. “