Arcas led them along a dry river course. The big black robots had no trouble negotiating the rough terrain, and neither did DD. Shadows from high, razor-edged cliffs closed in around them. Tinny echoes of their footsteps and voices sounded off the sheer walls. Rustlike impurities streaked through the rough rock, as if some primitive and bloody sacrifice had occurred on the ledges above.

Today, the orangish skies of Rheindic Co had a strange greasy quality, as if high smoke dimmed the sunlight. Margaret hadn’t bothered to study the planet’s quirky weather, but she thought the gauzy overcast looked a little odd.

She watched Arcas curiously as he hurried into the winding labyrinth, ducked to the left into a small side canyon, and climbed over rubble that had fallen from the cliffs. The stone walls narrowed even farther.

“This direction,” Arcas said. “Not too far.”

Louis pointed up toward the narrow slice of sky between the enclosing canyon walls. “I don’t like the look of that.”

Overhead, the smear of gray haze had clotted into hard fists of clouds sheeting feathery gray moisture. The slurry of rain and dust that fell from the clouds evaporated before it could strike the ground, and then came down in a renewed downpour.

“That looks like quite a storm.” Margaret glanced around at the canyon walls that seemed to bottle them up. “You don’t suppose Rheindic Co is one of those worlds that gets a year’s rainfall all in a single afternoon?”

Arcas sniffed the air with concern. “I wish I could touch one of my treelings and access information from the worldforest. I don’t know enough about deserts yet.” He looked around. “But let us hurry. The cliff wall is just ahead.”

They picked up their pace, climbing over boulders until they reached another finger canyon. Margaret wondered how Arcas had ever found this place and then traced his way back to camp. Now she did see a squarish cave opening high up on the crumbling cliff wall, where parts of a sealed overhang had fallen away. The rubble lay in chunks of debris on the canyon floor.

Even from here the cliff appeared hollow, more than just an arched indentation. When she looked just right, in the light and shadows of the gorge she could indeed discern something inside the cave, angular forms that did not look like natural rocks or cave growths. “Let’s climb,” she said.

The striated rock bands could provide a route for agile climbers to scale the face. DD had brought detachable pitons and wall-hugger attachments for his masters to use, but still it looked like a difficult ascent.

“DD,” Louis said, “you go up first and show us the way. Watch out for any unstable cracks or boulders.”