‘I know how these tales go,’ she said, still walking, slipping back out of the Language and into English again. ‘The woman buys nine pairs of iron shoes, and nine iron loaves, and nine iron staves, and she walks the length and breadth of the earth until the shoes are all worn through, and the staves are as thin as matchsticks, and she has eaten up every last scrap of the loaves, and only then does she find what she is looking for. But this is a different story.’

The door was abruptly ten paces closer. Still out of reach. But closer.

‘Once, in a long-distant state, there was a horse that galloped across land and sea … ‘ Irene began. She remembered the story well enough from Aunt Isra’s gathering. It was a standard myth, and that was part of its power. She kept on walking as she recited the story, and the door still stayed the same distance away: too far for her to reach, but close enough to tantalize.

Finally she came to the end. ‘From world to world he rides, from the gates of story to the shores of dream, until the world is changed and the horse is freed.’ She let the words hang in the air for a moment. ‘Until the horse is freed, the story says, which means that there must come a point when the horse is freed. And it must mean that the horse can be freed.’

The door jumped forward again in another blink of perspective. It was right in front of Irene now, almost close enough for her to walk through, but every step kept it one pace ahead of her.

Cold sweat trickled down her back. It’s listening to me. I’d better be able to give it what I’m promising, or this particular narrative is going to get very messy, very fast.

‘Of course,’ she went on, ‘in this story the heroine doesn’t necessarily know exactly how to free the horse. But the horse can usually point her in the right direction. Removing a collar, for instance, or undoing a bridle. And of course there’s usually a reason why the heroine wants to free the horse. You only get a kind-hearted heroine who unties the horse just because it looks unhappy in certain stories. I don’t think this is one of those stories.’

The door stayed at the same distance from her.

‘So, the story … ‘ Irene stopped walking. Without the sound of her footsteps, the corridor was even more ominously silent. ‘The young woman was in a strange land, and she looked around for help, for …’ It should have been her true love - that would have been one of the standard modes for a story of this type - but that wasn’t true of her and Kai. Even if there was wishful thinking on that subject. But that didn’t matter. She couldn’t risk a lie. Not if she was speaking in the Language.

‘The king’s son had been stolen, and she had come across land and sea to find him, in borrowed shoes and a borrowed dress, with no true friend at her side.’ The words stung in her mouth, true in their way, yet also just a story. It was like eating sherbet and feeling it pop in her mouth and rattle in her skull and ears. Her head was buzzing with it. ‘And she said, “I shall rescue him from the prison where they have kept him, and together we shall flee from his enemies and stop a war.” But she was sore afraid, for the whole city would rise to pursue them, once the king’s son was free from his prison.’

It was harder now. Irene had never tried this before, never thought of trying it before. But the Language was a tool, and her will was behind it, and this place was fragile, weak, easy to force. She wasn’t telling any lies. She was just telling the truth in a different way. ‘And as she walked down to the sea, she saw a chained and bridled horse, and said, “Would that I were as swift as you, so that we could escape!” And then the horse spoke to her, saying …’

It was as if she’d been playing a violin solo before, and now the rest of the orchestra came in on the beat, in a sudden weight of music that pushed down on her and shuddered through her body. She flung out her arms to either side to brace herself on the walls of the passage, struggling for breath as the crushing pressure seemed to catch at her chest, forcing her to breathe in its rhythm. The air in the passage shivered like the surface of a drum.

‘FREE ME FROM MY BRIDLE AND REINS,’ the voice shuddered around her, so loudly that she could barely make out the separate words, ‘AND I SHALL BEAR YOU OVER LAND AND SEA TO YOUR OWN HOME.’

Irene was opening her mouth to say yes without even thinking about it, carried along by the flow of the story, but then she dug in her mental heels and struggled to form different words. She had to set up this bargain to get what she needed. Once it was struck, there would be no chance to go back and renegotiate. Although the Train was still and unmoving, the sound of spinning wheels and clanging engines echoed in her ears, as if it was straining to haul some distant weight. ‘Most noble horse,’ she finally forced out. ‘I thank you for your offer. I beg that you allow me to go and find the prince and, when I return with him, I will free you. And you will bear us both back to the land from which we came.’

She’d been afraid of chaos contamination before. She’d been touched by it in the past, had it running in her veins, and it had nearly crippled her before she’d forced it out. What would it do to her, if she made a bargain with this creature?

‘YES …’ the voice breathed around her, in a vast exhalation that physically tore at her hair and clothing, dragging her forward so she could no longer keep her balance, but went stumbling through the doorway before her into the next carriage. Her back, her wrists and the pendant round her neck all seemed to be burning. Her Library brand, Silver’s bracelets and the pendant from Kai’s uncle - each objects of power in their own way - were struggling with the new bond she had willingly undertaken. She wasn’t in a train carriage, she was falling into darkness, and she was burning …