Even that gentle touch sent a shockwave of pain racing along her limb, but she bit her lip and forced herself to remain utterly still.

Then, with a quickness which surprised her, the boy wrapped his hand around hers. She gasped in pain, went to jerk it away, but then a sliver of light shot out from between their two hands, and the pain ebbed, then disappeared.

Just like that, the burning sensation was gone.

Tab's free hand flew to her mouth. The boy released her hand and crawled back to the wall, not taking his eyes off her.

Tab looked down at her hand. It was still blackened and ruined, but the wound was now… old. As if it had happened weeks ago. She looked up at the boy. ‘What did you do?’

There was the tiniest of shrugs.

‘Do you… do you have a name?’ she asked, barely above a whisper.

Nothing. Then the boy's lips moved. Tab bent closer, and this time she heard it.

‘Torby.’

Tab sat back and smiled. ‘Thank you for fixing my hand.’ She wished fervently that she could heal Torby's wounds, knowing that healers couldn't cure their own injuries.

Tab woke later that night to find a small warm body pressed against her. Very slowly she rolled over. Torby whimpered but did not wake or leap away in alarm. She made sure he was covered with a blanket then slid her arm around his shoulders, and held him tightly as her eyes filled slowly with tears.

What's going to happen now? she wondered bleakly. Because one thing was very clear to her: she had to escape from this place, and she had to take Torby with her.

Shockingly cold water hit Tab's face. She sat up, gasping and spluttering. Immediately she was aware that Torby was gone. She looked about frantically. He was nowhere to be seen.

In a fury that took even the boy-king by surprise, she leapt off the bed and attacked him. Momentarily stunned, he took a step backwards, then regained his composure and laughed, holding her off with ease.

The next second a guard grabbed her from behind and threw her back on the bunk where she crouched, snarling. Kull clicked his fingers and another guard stepped into the cell doorway, holding Torby. Tab held out her arms and Kull nodded. The guard released the boy and he hurtled across the cell and into Tab's arms, burying his face against her shoulder, his body trembling.

‘What did you do to him?’ shouted Tab.

Kull seemed amused. ‘Nothing,’ he said. ‘Not today at least, and it can stay that way – if you cooperate.’

Tab's sharp intake of breath was the only sound in the cell. So that was why they had moved her. They hadn't gotten what they wanted by torturing her so they had tried something different.

‘Well?’ said Kull. ‘I'll ask only once. Where is the magicians’ icefire?’

Tab slumped. This was all her fault. If she hadn't been stupid enough or arrogant enough to think she could handle the Tolrushian spies, she wouldn't be here now. But then she wouldn't have found Torby either…

She sighed, and told them exactly where she had hidden the gem that she'd stolen from the magicians.

Kull smiled broadly. ‘See, how hard was that?’ He suddenly frowned and pursed his lips. ‘Tell me, riftling. Why didn't you hand over the icefire to your Navigators’ Guild?’

Tab slumped with her betrayal. ‘I was going to but as time went by I knew no one would believe my story. And even if they did, they would have blamed me for everything. I had… had intended to leave it in the Chief Navigator's office… but -’

Kull slapped his thighs with merriment. ‘Enough, you fool of a child. For a moment I thought perhaps the icefire was faulty. Instead you worried about your own safety and have caused a two-fold calamity for your city!’ He turned to go.

‘What about us?’ said Tab. ‘You've got what you wanted… ’

‘We'll see,’ said Kull. ‘Perhaps the gem is where you say it is, and perhaps it isn't.’

He turned and strode out of the cell and the guards followed him. The cell door clanged shut with an ominous sound. Tab held Torby as tightly as she could. She suspected there was almost no chance that Kull would release them, even when he had the gem. Much easier just to slit their throats and throw them overboard.

Torby raised his face and looked at her. ‘You knew.’

She smiled down at him. ‘Yes. I went back to the slaughterhouse and grabbed the icefire. Only just in time, too, because Fontagu turned up about two minutes later. I don't think he saw me. I snuck out and hid the gem where nobody could find it.’

‘Why?’

It hit her then that Torby was actually talking. She felt like laughing, as if he were her own child, or a little brother, and these were the first words he had ever spoken. The feeling caused an odd ache in her chest.

‘Because I thought that it was the most dangerous thing in the whole world. And I was right. It ripped my home, Quentaris, from out of the very ground and threw it through a rift vortex, into another universe. Later, I realised what the icefire really was: a source of fuel. But by then I'd waited too long to hand it back to the magicians. And the longer I waited, the more impossible it was. But I really was going to leave it in Stelka's office.’

Torby was silent for a while, then he said, ‘What now?’

‘I don't know, Torby. I really don't know.’

She kept hoping that Kull, once he had the icefire, would release them. But that hope was dashed that evening. Kull himself, alone, came to gloat. He even bowed low to her.

‘Truly,’ he said, ‘I am in your debt. Never have I seen such an icefire gem! My magicians tell me it will power the ire ore for at least a year, maybe more. With it we will capture and crush Quentaris, and we will extract the secret of how to get home again. So once more, apprentice, I thank you.’

He bowed a second time, smirking.

‘If you are in my debt then I ask that we be released.’

Kull stared at her for a moment then burst out laughing.

‘You can't keep us here!’ she cried. ‘And anyway – Quentaris will send somebody to rescue us.’

Kull stopped laughing and his eyes glittered with malice. ‘Are you threatening me, brat?’

Tab's eyes went wide. She looked away from his gaze. ‘No,’ she said. But then she looked up again, defiant. ‘But they will come for me.’

‘Why, because you saved them?’ asked Kull. He emitted a scornful bark of laughter. ‘A creature like you lives to serve its city, not the other way around. Do you really believe Quentaris feels any loyalty towards you? Know this, even now they are making speed away from us. Besides, your name there is mud, thanks to the vigorous efforts of my… agent.’

‘You're a liar,’ said Tab.

Kull's face flushed and he gripped the cell bars. Tab knew that if it had not been for those bars he would have killed her on the spot. Finally, after a long panting moment, he took a step back, smirking.

‘Tomorrow morning, you will be given a breakfast fit for royalty,’ he said. ‘Then you will provide the day's entertainment. My nobles and I, you see, are in disagreement over exactly how high above the ground we are. And my master magician has come up with a delightful way to measure our altitude.’

Tab scowled and said nothing. She pressed her hands over Torby's ears so he couldn't hear.

‘Apparently, sound travels at a fixed rate of speed. So my master magician has determined that by throwing a child overboard and timing its screams as it falls, we will be able to arrive at an exact measurement. Rather brilliant, I thought.’

And with that, Kull turned on his heels and strode out of the cell block, whistling merrily.

The night deepened. Tab dozed fitfully and woke to the sound of a distant bell tolling midnight. And with the final peal, the first threads of a plan began to knit in her mind. She woke Torby…

Tab cleared her mind, and tried to recall what it felt like to be a rat, to be so small and scared, and always so hungry. She pictured the twitching whiskers on the snout, the feel of a tail stretching out behind, and she let her mind float outwards… and almost at once she was there, inside the rat, peering out from its eyes. It was reaching up a wall as though curious. Smells and sounds leapt at her. She forced the rat to look around and suddenly she gasped. She could see herself – only that wasn't what she looked like. To the rat, she was a tall, thin blob with a pale face and sharp horrible eyes. She was also black and white; the rat, like all rats, could not see in true colours.