The footsteps came closer. Taking up Haani, Tiaan staggered into the archway directly opposite. Spheres lit up, revealing a stone passage that curved away into darkness.

On she trudged, along a passage that seemed to have been curving forever. Tirthrax was unfathomable. It was as if she was inside an exuberant work of art, built solely for the pleasure of mastering its materials.

Her mouth was powder dry. She had not had a drink since opening the gate, a day and a night ago. Another passage slashed across the first and she turned left into it, but some twenty or thirty paces along, the passage ended in native rock. Or did it? As she headed back, from the corner of her eye the rock seemed to shift sideways into a cavity darker than black itself. She moved towards it, thinking it might be a place to hide. The blackness went back to rock.

Tiaan reached out with her free hand. Rock, unquestionably, but again as she moved her head came that flash of blackness, like a tunnel extending into the mountain. The moment she looked directly at it, it changed back into wall.

She turned her head back and forth. Blackness, wall, blackness, wall. Could she get through? There was an enchantment here and since Nish had no talent for the Art he probably could not follow.

Tiaan touched the crystal hanging on a chain around her neck – just an ordinary hedron — thinking it might help her to see more clearly. The rock vanished and a black tunnel opened up before her. She edged inside.

After several minutes, the blackness gave way to a faint glow which had no particular form, but quivered gently. It felt more like a soap bubble, but gave before her, sliding wetly over her fingers.

Any refuge was better than none. Tiaan pushed into the clinging stuff, its resistance broke and she was through. It was even colder here, and so dark that she could see nothing but the shimmering edges of a second bubble, a cube with curved faces that contained within it another, smaller cube, and inside that another, and another, and another. The hair stirred on her head. Infinity blocked her way – infinity and nothingness. This was a forbidden place.

She spun around but behind her now felt like rock, even when she touched her hedron. Tiaan moved toward the cubic bubble. Its walls began to wobble, and so did the inner cubes, vibrating faster and faster until she could no longer see them.

Shifting Haani on her shoulder, Tiaan lowered her head and pushed at the bubble. The wall parted but inside was like the previous one, though smaller. Her head touched the upper face of the cube, which was freezing. The nested cubes extended to an infinity that frightened her.

Since there was no way back, Tiaan pushed through the wall of the next cube. The first breath burned her lungs. With the next, she felt frost forming in her nostrils. She tried to back out but the wall resisted her. Panicking, she kicked the face of the cube in front of her. It was much more solid – more like flexible glass than bubble – and her sandal bounced off.

Steadying Haani, Tiaan lifted the hedron over her head. At once she saw the coloured energy patterns of the field swirling around her like a psychedelic tornado. She drew power into the hedron and reached out. As her fingers touched the wall, it thinned, so she scored the crystal across and back. The bubble vanished with a faint tinkle and a blast of freezing air. One by one, the other cubes popped until the tunnel lay open before her. Unfortunately it was also open behind. The illusory barrier had disappeared.

Some distance along, she emerged in an open cavern of rough-hewn stone shaped like a cone standing on its base. It was strikingly different from the rest of Tirthrax, where the stone had been carefully polished and intricately decorated. The rock here looked deliberately unfinished.

The cavern was dimly lit by something circular, high on one wall. Her eyes adjusted. It was a shaft that ran up through the mountain at a steep angle. Icicles hung from its lower lip and the light was daylight, deep blue as if filtered through ice. It must be morning outside.

Moving on, she passed through a blue corona like illuminated mist, though more solid. She distinctly felt its resistance. It was one of a series of concentric coloured rings lit by the light from the upper shaft. Each ring was a deeper hue than the one surrounding it. A circle of indigo, almost black, filled the centre. Tiaan pushed through the rings and almost fell into another shaft, a continuation of the first.

Laying Haani beside it, she peered down. The shaft was a smooth bore through the rock, its sides as polished as glass. She could not tell how far it went, though wisps of dark mist coiled lazily around the walls, and in the depths it had the look of a frozen whirlpool. She wondered what it would look like if it unfroze. Taking up a chip fallen from the ceiling, she dropped it in. It clicked off the sides a couple of times, she heard nothing for thirty or forty heartbeats, and at last a frosty tinkle. The shaft was deep. It would do.

The sounds came echoing back in reverse order: the tinkle, and a long time later the clicks, greatly magnified. The last click thundered out, whirling the coloured rings about, and silence fell once more.

The child looked to be sleeping but her little chest was sunken, the broken ribs driven into her lungs by the blow from the javelard. A smear of blood tinged her lower lip. Tiaan wiped it off, smoothing the pale hair with her fingers.

Taking Haani in her arms, she sat beside the shaft, rocking. A tear trickled down one cheek. Little Haani had been the happiest of children, living a carefree life with her mother and aunts by the lake, until Tiaan came. Until the nylatl – a creature of mad savagery – gorged itself on Haani’s mother and aunts. The awful memories went round and round.

‘There she is!’

Nish’s cry of triumph reverberated from the tunnel. Tiaan was still cradling Haani and, before she could move, he threw himself at her.

Haani fell beside the shaft. Nish forced Tiaan’s arm up behind her back so hard that she cried out. She kicked with her heel, striking him on the shin. He yelped but did not let go. As she tried to pull free, one foot went over and a pain sheared through her guts at the thought of falling. No, dying was all she had left. Tiaan threw herself into the bore.

Nish landed hard on his knees and cried out. She made no noise, nor tried to save herself, as she swung on his arm. He was a small man, not much taller than she. He could hardly hold her for long.

Her wrist slipped. ‘Let me go, Nish.’ Tiaan forced herself to speak calmly. ‘I want to die.’

Nish’s hard fingers bit into her wrist. ‘I’m sure you do!’ Perspiration beaded on his eyebrows, freezing even as she watched. ‘You’ve betrayed your friends, your family, your manufactory and your world. I won’t let you die.’

‘Please, no,’ she begged.

‘I’m taking you back – for justice!’

‘Revenge,’ she gasped. ‘That’s all you care about.’

‘Whatever!’ He strained with all his strength.

Terror seized Tiaan. She could imagine the nightmare trip back to the manufactory, Nish tormenting her all the way. She would be paraded before her thousand former workmates, and down in her home town of Tiksi in front of her vindicated mother. After a public trial she would face a drawn-out execution, a gruesome and grisly spectacle by some method officially prescribed for the artisan she had once been. All would be lovingly recorded in the Histories and a hired teller would turn it into a cautionary tale, that the whole world know of her crime and its punishment. The Council of Scrutators required everyone to know their justice, and to fear it.

Thrashing her legs, Tiaan tried to make him drop her. Terror twisted his face as he was dragged closer to the edge. One knee slipped over. She would never have expected such desperate courage from Nish. Why didn’t he let her go?