"Faster!" Paul gasped.

The first rock shingle, like a beach slanting from the sand, lay no more than ten meters ahead when they heard metal crunch and shatter behind them.

Paul shifted his pack to his right arm, holding it by the straps. It slapped his side as he ran. He took his mother's arm with his other hand. They scrambled onto the lifting rock, up a pebble-littered surface through a twisted, wind-carved channel. Breath came dry and gasping in their throats.

"I can't run any farther," Jessica panted.

Paul stopped, pressed her into a gut of rock, turned and looked down onto the desert. A mound-in-motion ran parallel to their rock island--moonlit ripples, sand waves, a cresting burrow almost level with Paul's eyes at a distance of about a kilometer. The flattened dunes of its track curved once--a short loop crossing the patch of desert where they had abandoned their wrecked ornithopter.

Where the worm had been there was no sign of the aircraft.

The burrow mound moved outward into the desert, coursed back across its own path, questing.

"It's bigger than a Guild spaceship," Paul whispered. "I was told worms grew large in the deep desert, but I didn't realize . . . how big."

"Nor I," Jessica breathed.

Again, the thing turned out away from the rocks, sped now with a curving track toward the horizon. They listened until the sound of its passage was lost in gentle sand stirrings around them.

Paul took a deep breath, looked up at the moon-frosted escarpment, and quoted from the Kitab al-Ibar: "Travel by night and rest in black shade through the day." He looked at his mother. "We still have a few hours of night. Can you go on?"

"In a moment."

Paul stepped out onto the rock shingle, shouldered the pack and adjusted its straps. He stood a moment with a paracompass in his hands.

"Whenever you're ready," he said.

She pushed herself away from the rock, feeling her strength return. "Which direction?"

"Where this ridge leads." He pointed.

"Deep into the desert," she said.

"The Fremen desert," Paul whispered.

And he paused, shaken by the remembered high relief imagery of a prescient vision he had experienced on Caladan. He had seen this desert. But the set of the vision had been subtly different, like an optical image that had disappeared into his consciousness, been absorbed by memory, and now failed of perfect registry when projected onto the real scene. The vision appeared to have shifted and approached him from a different angle while he remained motionless.

Idaho was with us in the vision, he remembered. But now Idaho is dead.

"Do you see a way to go?" Jessica asked, mistaking his hesitation.

"No," he said, "But we'll go anyway."

He settled his shoulders more firmly in the pack, struck out up a sand-carved channel in the rock. The channel opened onto a moonlit floor of rock with benched ledges climbing away to the south.

Paul headed for the first ledge, clambered onto it. Jessica followed.

She noted presently how their passage became a matter of the immediate and particular--the sand pockets between rocks where their steps were slowed, the wind-carved ridge that cut their hands, the obstruction that forced a choice: Go over or go around? The terrain enforced its own rhythms. They spoke only when necessary and then with the hoarse voices of their exertion.

"Careful here--this ledge is slippery with sand."

"Watch you don't hit your head against this overhang."

"Stay below this ridge; the moon's at our backs and it'd show our movement to anyone out there."

Paul stopped in a bight of rock, leaned the pack against a narrow ledge.

Jessica leaned beside him, thankful for the moment of rest. She heard Paul pulling at his stillsuit tube, sipped her own reclaimed water. It tasted brackish, and she remembered the waters of Caladan--a tall fountain enclosing a curve of sky, such a richness of moisture that it hadn't been noticed for itself

. . . only for its shape, or its reflection, or its sound as she stopped beside it.

To stop, she thought. To rest . . . truly rest.

It occurred to her that mercy was the ability to stop, if only for a moment.

There was no mercy where there could be no stopping.

Paul pushed away from the rock ledge, turned, and climbed over a sloping surface. Jessica followed with a sigh.

They slid down onto a wide shelf that led around a sheer rock face. Again, they fell into the disjointed rhythm of movement across this broken land.

Jessica felt that the night was dominated by degrees of smallness in substances beneath their feet and hands--boulders or pea gravel or flaked rock or pea sand or sand itself or grit or dust or gossamer powder.

The powder clogged nose filters and had to be blown out. Pea sand and pea gravel rolled on a hard surface and could spill the unwary. Rock flakes cut.

And the omnipresent sand patches dragged against their feet.

Paul stopped abruptly on a rock shelf, steadied his mother as she stumbled into him.

He was pointing left and she looked along his arm to see that they stood atop a cliff with the desert stretched out like a static ocean some two hundred meters below. It lay there full of moon-silvered waves--shadows of angles that lapsed into curves and, in the distance, lifted to the misted gray blur of another escarpment.

"Open desert," she said.

"A wide place to cross," Paul said, and his voice was muffled by the filter trap across his face.

Jessica glanced left and right--nothing but sand below.

Paul stared straight ahead across the open dunes, watching the movement of shadows in the moon's passage. "About three or four kilometers across," he said.

"Worms," she said.

"Sure to be."

She focused on her weariness, the muscle ache that dulled her senses. "Shall we rest and eat?"

Paul slipped out of the pack, sat down and leaned against it. Jessica supported herself by a hand on his shoulder as she sank to the rock beside him.

She felt Paul turn as she settled herself, heard him scrabbling in the pack.