She sprang up onto the rail, crouched there for an instant, gathering herself. She did not think. Thinking would have been madness. She leapt into empty space, limbs flailing. The whole machine wobbled and swayed as she caught hold of its outermost ring. She swung underneath, hanging breathless. Slowly, delicately, her tongue pressed into the roof of her mouth, she pulled herself up by her arms, hooked her legs over the metal and dragged herself along it. Soon it brought her close to a wide disc, scored with grooves, and she clambered from one to the other, body trembling with effort. The cool metal quivered under her weight, twisting and flexing, wobbling with her every movement, threatening to shrug her off into the empty void. Ferro might have had no fear in her.

But plunges of a hundred strides onto the hardest of hard rock still demanded her deep respect.

So she slithered out, from one ring to another, hardly daring even to breathe. She told herself there was no drop. She was only climbing trees, sliding between their branches, the way she had when she was a child, before the Gurkish came. Finally she caught hold of the innermost ring. She clung to it, furious tight, waiting until its own movement brought her close to the centre. She hung down, legs crossed around the frail metal, one hand gripping it, the other reaching out towards that gleaming black ball.

She could see her rigid face reflected in its perfect surface, her clawing hand, swollen and distorted. She strained forward with every nerve, teeth gritted. Closer, and closer yet. All that mattered was to touch it. The very tip of her middle finger brushed against it and, like a bubble bursting, it vanished into empty mist.

Something dropped free, falling, slowly, as if it sank through water. Ferro watched it tumble away from her, a darker spot in the inky darkness, down, and down. It struck the floor with a boom that seemed to shake the very foundations of the Maker's House, filled the hall with crashing echoes. The ring that Ferro clung to trembled and for a giddy instant she nearly lost her grip. When she managed to haul herself back she realised that it had stopped moving.

The whole device was still.

It seemed to take her an age to clamber back across the motionless rings to the topmost gallery, to make the long descent down the towering walls. When she finally dropped to the floor of the cavernous chamber her clothes were torn, her hands, elbows, knees grazed and bloody, but she scarcely noticed. She ran across the wide floor, her footsteps ringing out. Towards the very centre of the hall, where the thing that had fallen from above still lay.