There was a sound behind him like the breath of a huge animal.

He twisted around and stabilized — and found his eyes filled with orange light.

The Gap between Shell and Home was unbroken. The two worlds’ darkling daylight was begrudged them by a Sun, a mottled sphere a mile across — a sphere that now twisted and rolled through the sky towards Teal…

…But it was going to pass miles above him.

Cursing, Teal labored at his burners. The balloon yanked him upwards, but soon the harness’s pressure began to ease. He was approaching the middle of the Gap: the place halfway between the worlds where weight disappeared. He knew that if he continued his ascent, “up” would become “down"; Home would turn from a roof to a floor, and the place where Teal had been born would once more become the Shell over Home, the world that his grandmother’s mother had known.

The Sun’s breath became a roar.

He used a soaked cloth to dampen the burners, trying to hover just below the zone of complete weightlessness. The guide rope creaked; the balloon bobbed in a gust hot enough to scour the frost from his face, and he turned to the Sun once more.

It came at him like a fist. Boiling air fled its surface. His craft tossed like a toy. His eyes dried like meat in a fire and he felt his face shrivel and crack.

The guide rope snapped with a smell of charred leather. His balloon flipped backwards once, twice, seams popping. He roared out his frustration at the impossible thing—

Then the balloon was falling. He caught one last glimpse of the Sun as it passed above him, splinters of ruddy light stabbing through slits in the battered envelope.

He fell back through the clouds. Snow battered his scorched face as he labored at the burners, striving to replace the hot air leaking out of the envelope.

Soon he could make out the bridge anchor site, now surrounded by fallen miles of rope. There was patient Orange running in little agitated circles, and a bearded man standing there hands on hips, shouting something — Damen, it must be — and now Damen was running towards the point he would hit, a mile or so from the anchor.

The ground blurred towards him. He closed his eyes and tried to hang like a doll, soft and boneless.

The earth was frozen and impossibly hard. It seemed to slam upwards and carry him into the sky, sweeping up the wreckage of his balloon.

Damen carried Teal to his teepee and dumped him onto a pallet. Erwal ran to them and stroked Teal’s face.

Overwhelmed with guilt Teal tried to speak — but could only groan as broken things in his chest moved against each other.

Damen’s bearded face was a mask of contempt. “Why? You useless bloody fool, why?”

Something bubbled in Teal’s throat. “I… I was trying to fix…”

Damen’s face twisted, and he lashed the back of his hand upwards into his brother’s chin. Teal’s back arched. Erwal tugged at Damen’s arm.

Damen turned away. He walked with Erwal to the teepee’s open entrance, speaking softly. He cupped her cheek in his massive hand… and then ducked out of the teepee. Erwal tied up the flap behind him.

“Erwal… I…”

“Don’t talk.” Her voice was harsh with crying. She bathed his face.

He closed his eyes.

When he woke it was night. His grandmother was watching over him, her face a wrinkled mask of reassurance in the alcohol lamp’s smoky light.

“How are you?”

Teal probed, wincing, at his ribs. “Still here. Where’s Damen?”

Allel rested a birdlike hand on his shoulder. “Not here. Take it easy.” She laughed softly. “What a pair. You, the hopeless dreamer… just like I was at your age. And Damen reminds me of my mother. A hard-headed, practical, obstinate — so-and-so.”

The old woman’s quaint Home accent was like balm to Teal. He struggled to sit up; Allel arranged the blanket of soft leather over Teal’s bound-up ribs. “You’re not too badly hurt,” she said. “Just a bit flattened. Your wife’s left you some broth: boiled-up mummy-cow meat buds. See? Come on, let me feed you.”

“Thanks…”

Allel pulled a stone knife from her belt. She’d owned that knife all Teal’s life; Teal knew it was one of the few remembrances Allel had brought with her on her last journey from her home world. Now she used the blunt edge of the knife to ladle broth into Teal’s cracked mouth.

“She worries about you, you know. Erwal.”

Teal nodded ruefully through the food.

“Not good for her in her condition.” Allel’s voice was as dry as a rustle of leaves.

“I know. But I had to go, you know, grandmother. I had to try—”

“To save the world?” The old woman smiled, not unkindly. “Yes, just like I was… or,” she continued, “perhaps you are a bit tougher. I crossed the Gap with my mother — that was adventure enough — but I’d never have dreamed of challenging the Sun itself…”

Allel’s rheumy eyes peered into the wavering light of a lamp. “There are so many differences between Home and Shell. We had no mummy-cows to feed us, you know. Only cow-trees. And we spoke a different language. It took me long enough to learn yours, I can tell you, and my mother wouldn’t even try…

“I wonder if all these differences were intended, somehow. Perhaps the Sun was meant to fail. Perhaps there’s a plan to force us to cross the Gap, to mix our blood and toughen ourselves—”

Teal pushed away the knife and lay back on his rustling pallet. He’d heard all this before. “Maybe, but such speculation won’t help us find a way out of the trap the world’s become. Will it?”

Allel shrugged mildly. “Perhaps not. But the alternative is ignorance — which can only drive you to spectacular suicide. Such as by crashing into the Sun in a leather balloon.”

Teal found himself blushing under his blisters.

“Before you can find a way out of the world you need to understand its nature.” She wagged a bony finger. “Are you prepared to be a little patient, and do a bit of thinking?”

Teal smiled and propped himself up on one elbow.

Allel put aside the bowl of broth and settled herself onto a mat beside the pallet, cross-legged. “When I wasn’t much younger than you, my mother took me on a long walk to an old abandoned City to the north of Home. And there I learned something of the nature of our world.

“The world is a box. We locked ourselves into a huge box to escape from the Xeelee, whatever they are. But the nature of this box is quite remarkable.”

Teal gathered the blanket tighter around his aching chest. “Go on.”

Allel pulled up a section of the leather mat beneath her and bunched it into a rough globe. “Here’s a model of the world. Let’s imagine there are insects living on this globe.” Her fingers trotted comically over the globe; Teal smiled. “They’re perfectly happy in their little world, never imagining the mysteries above or below them. Yes?

“Now. I think the world we came from is a flat place, somewhere… else. Just like the rest of this mat — a flat place that goes on forever, and contains stars and Xeelee.”

She pointed at the place where the globe joined the mat, encased in her spidery fist. “The worlds must touch, as these models do here. We have to find such a place. A place where you can walk out of our world and into the original… a door to fold through.”

Teal nodded slowly. “Yes — yes, I understand. But where would such a door be?”

“Ah.” Allel smoothed the mat and stretched her withered legs. “That’s the question. Surely it could only be in one of the old Cities, at the northern extremes of the worlds… But nobody on either world knows of anything that sounds remotely like a door. No human, anyway.”

Allel dropped her eyes, wrinkles clustering around her mouth. “And there’s another question. Sometimes I think it would be better not to find the door. There’s so much we don’t know about the past. Why not? Suppose it’s been deliberately forgotten. Suppose we shouldn’t try to find out about the world, the Xeelee… about ourselves. Perhaps it’s better not to know—”