Allel inspected paint dust. “This is just dyed cow-tree milk. This last picture must have been added much later—”

Boyd swore. She spat on the smooth floor and stalked out.

…And, thought Allel, excited, in that case maybe the world was more like the other image, the blue sphere. But what did it mean? Everyone knew there was a Shell around the world — you could see it…

She became aware of her mother’s absence. Cursing, she hurried out.

Boyd stood a few paces from the door, fists clenched. Feathers of snow drifted around her legs. “I repeat. Why do you think I brought you here?”

Allel tried to concentrate on the question. “To show me this place? To tell me its story?”

“Yes!” The trackless snow softened Boyd’s shout. “Once we rebuilt the whole world, but now we can’t even melt a few glaciers.” She gripped her daughter’s shoulders, not roughly. “People got soft and forgot. Allel — if I fail, you’ve got to carry on. Perhaps it will fall to you to take over, and lead our people to the Bridge. That’s the truth of our world, the only truth. The only way to save ourselves that’s within our power.”

Allel returned her mother’s fierce stare. “I understand, but…”

Boyd sneered: “But you want to ask the Shell dwellers what it’s like living in a saucer.” Her eyes were flat, impervious to the hard cold. Allel wondered how she and her mother had grown so far apart, becoming as symmetrical as opposing poles. The one pragmatic, the other — a visionary? — or a fool? Who was right? Perhaps that was a question without an answer—

She knew Boyd was trying to force her to grow up. But the Shell arced over them like a roof coated with its own ice. Could she give up all her dreams and become a creature of her mother?

“Listen,” she said desperately. “I’ve thought of a way we can take the Bridge.”

Her mother whirled and drove her palm against Allel’s cheek. Blood pumped into Allel’s mouth and strange scents flooded her head.

“You’ve learned nothing,” Boyd said hoarsely. “I’d rather leave you here.” She forced herself forward, fists clenched white.

Allel mumbled: “I mean it.” She felt blood freezing on her lip. She became aware she’d lost her cap. But Boyd was hesitating.

“How?”

“If I succeed…” She coughed and spat blood. It was vivid against the snow. “If I succeed, will you help me build a hyperdrive machine to fly to the Shell?”

Boyd’s eyes narrowed. “I don’t believe it. You’re bargaining with me…” Then she dug a bark handkerchief out of a voluminous pocket. “Here. Clean yourself up.”

The dozen warriors converged on the Bridge. They wielded branches hacked from cow-trees, their miraculous meat buds smashed away. To Allel, watching from above, the crude clubs were symbols of the depressing symmetry of humanity’s rise and fall.

The Bridge was a gleaming parabola plastered with teepees. From the teepees defending warriors emerged, grubby and yelling, brandishing rocks and clubs. Blood splashed over the seamless carriageway. But soon it was hard to separate the two sides, but Allel could see that as before the attackers were being driven away.

The breeze picked up and the great balloon over her creaked into motion, its stitched bark straining. The canvas sling chafed her armpits, and she tended the alcohol burners clustered like berries just above her head. The balloon wallowed in the air. Soon its load would be lighter, she thought, uncertain of her feelings.

Her shadow drifted over the melee, touching fighters, men and women alike, who wriggled together like blood-soaked termites. They looked up in fear or anticipation. She took a small alcohol lamp, one of a cluster tied to her belt. She lit the lamp, cut its cord with her stone knife, and dropped the lamp delicately into the defenders’ muddled line. The lamp flared into flame; a toy man ran screaming, his shirt a torch. Another lamp, and another. Cries of anger sailed up at her, followed by whirling clubs. No weapons could reach her, and she dropped her lamps. Then the defenders’ line broke and the battle surged across the Bridge. Teepees crumpled, and old folk screamed. Allel thought she heard her mother shout in triumph.

Her lamps gone, Allel dropped the pouch and the balloon rose further. She stared up at the Shell’s complex tapestry and waited for a breeze to take her home.

She found the teepee’s air filled with her mother’s sweat and dirt. Boyd’s left wrist was a stump of torn blood vessels and shattered bone. It had been cauterized; now Lantil bathed it with milk and tears. Boyd took Allel’s forearm in a grip that pulsed with pain. “Daughter! Your damn bag of smoke worked…”

Allel tugged gently, wanting only to be released. “Yes. And now you’ll have to help me build a real machine to cross the Gap.”

Lantil pushed at Allel’s chest, his liver-spotted hand fluttering like a bird. “You should be ashamed to speak to her that way. Can’t you see she’s hurt?”

But Allel kept her gaze locked with her mother’s.

Slowly Boyd grinned. “Won’t give up, will you? Determined to prove me wrong. All right. On one condition.”

“What?”

“Take me, too. I’ve done my job here; maybe I want to see the Shell people, too… ah…”

The pain silenced her. Lantil pulled his daughter’s blood-spattered head against his chest.

Allel loosened her mother’s grasp, and went to her pallet to start her plans. She lay with her face to the bark wall.

The whole village turned out for the launch. They nudged each other and pointed out panels on the balloon which they themselves had helped stitch, forgetting Boyd’s five years of bullying.

Impeded by their harnesses, Boyd and Allel labored at the bellows-like fuel pumps. The great bark envelope filled slowly, throwing swollen shadows in the flat morning light. Allel eyed the low Sun warily. They’d timed their flight to avoid a collision — fantastic though such a prospect seemed. But, she had reasoned doggedly, the Shell was behind the Sun. They were going to fly to the Shell. Therefore they could hit the Sun, and had to navigate to avoid it.

Her harness twitched twice, as if coming awake — and then, with a surprising surge, lifted her. The ground tilted away. People gave a ragged cheer and children chased the balloon’s shadow. Boyd roared and waved her good hand at them. Her crippled arm was lashed to the rigging. “We’re off, daughter!” she bellowed.

The landscape opened out and swallowed up the huddled villagers. To the north the Atad river curved into view, and beyond the site of their old home Allel could see the glaciers prowling the horizon.

She felt she was floating into a great silent box. The balloon’s throat occluded the Shell’s upside-down clouds. She hoisted herself into the rigging to tend the burners, prizing the stubby wicks from the resin-soaked barrels of alcohol. Gritty sweat soaked her eyes. She’d insisted they both wear quilted coats despite Boyd’s protests; she remembered the frozen ice-blue bird she’d found on Hafen’s Hill on another summer day, five years ago.

And sure enough, not many minutes later the dampness at her neck chilled and dried. Her breath caught and soon grew labored. “Even the damn air has a Gap here,” growled Boyd. “But you know, this harness isn’t chafing so much as it did.”

Allel, too, felt oddly light; she had a sensation of falling. But they rose smoothly into blue silence. Soon they were miles up; clouds dissolved as they passed into them. Their world collapsed to a Shell-like map, shutting them out; above and below became symmetrical and Allel’s stomach lurched.

Their rate of ascent slowed. The breeze in the rigging grew softer. The craft lumbered, unstable.

“What now?” demanded Boyd uneasily. “Watch the burners.”

“Yes. I wonder if — ah. The burners! Quick!”