Tiaan slipped around the corner to a washing trough, beyond which she spied another door. Could it be this easy? Ullii was paying her no attention. Edging it open, Tiaan found herself in a set of chambers like many she had seen in Tirthrax. She went through the bedchamber, out the far door and tiptoed around a gentle curve. Passages led three ways. Straight ahead lay a stair entirely made of glass. More extravagant than any she had looked at so far, it looped back and forth across the room like the flourishes on the end of a queen's signature. She would be seen on it from top to bottom. But it led up, and that felt right.

As Tiaan reached the first loop of the stair she heard Nish's bellow of rage. She bolted.

'There she is!' He took the glass treads three at a time, shaking the stair with every step.

She fled up and up. Nish gained slowly. At the top she encountered another stair, made of obsidian, then a third, a simple spiral barely wider than her hips. It was so steep that to look down caused sickening lurches in her stomach.

Light appeared above her. Daylight – a way out. She hauled herself up by her arms. A cavern opened out before her, a hemisphere scooped from the native rock of the mountain. The floor, walls and roof were like polished granite, the flat side a single sheet of glass five spans high. Outside lay a platform with a high-backed stone seat, and beyond that a sea of peaks and snow and ice went all the way to infinity. The sun was rising.

Tiaan ran up to the glass and stopped. It was inset into the stone on all sides. She pressed her hands against it but had to snatch them away – the glass was bitterly cold. If there was a door she could see no sign of it, nor any other way out. Putting her back to the glass, she waited. Nish was scarlet in the face, his step as unsteady as hers, but he drove himself on.