It was not possible. He hung above the furnace below, feeling the agonizing heat of the fire on his legs. Rosa lay on the floor, her bare arm hanging down into the burning chasm. Luke could only stare up at her, at her white face, at her wrist and hand holding his – impossibly small. There was no way she should have had the strength to even hold him, let alone catch him as he fell.

She had her eyes closed and her face was sheened with sweat.

‘Rosa!’ he gasped.

‘Shut. Up.’

He felt her nails digging into him. He could see her lips moving in some inaudible exhortation.

Slowly, slowly, she was dragging him back from the edge, pulling herself backwards along the floor, her lips constantly moving with a low litany. Her magic blazed around her, a fierce flaming gold, and suddenly he understood. Witchcraft. She was holding him by witchcraft.

He knew he should struggle. He knew what William and John and all the Brothers would say – that this was devil’s work. That it would be better to burn in life than be saved by such unholy means and burn in death. But he no longer cared. He no longer cared about anything except the unbearable heat of the fire on his smouldering boots, the stench of burning wool from his great coat, the flames eating away at the joists below Rosa, minute by minute.

He was almost there. He was almost to the edge. In another moment he would be able to swing his leg up, pull himself to safety . . .

But just as Rosa gave one last superhuman effort, the veins in her forehead standing out in desperation, her hair wet with sweat – there was a massive earth-shaking BOOM!

A roar, like a river bursting its banks.

An explosion that rocked the building to its foundation.

Concrete and bricks and burning beams tumbling around him – and he was falling. He felt Rosa’s magic wrap around him in a fierce embrace.

And then nothing.

When Luke opened his eyes he could see sky. It was not quite dawn, but there was a thin yellow light at the horizon, as if the sun could barely penetrate the river fog. He was lying on the cold ground with a beam digging into his spine and there were bricks and masonry scattered all around. His leg felt as if it might be broken. He couldn’t feel his arm at all and, when he tried to lift it, it wouldn’t move.

With difficulty he turned his head to see what was pinning it and his heart gave a great leap of hope and despair.

It was Rosa. She was lying on his arm. Her head was flung back, her white throat bare to the sky. Her hair was loose and straggled all around.

Her face, beneath the soot and blood and muck, was white – and her hand, when he touched it, was cold. There was not a single spark of magic around her.

A great sob forced its way up from his gut.

‘Rosa.’ He pulled her up, pulling her against him. ‘Rosa, what have you done? What did you do?’

He began to cry there, crouched in the deserted ruins of the factory. Her death solved everything. He was free. And he would have given anything to undo it.

‘I’m so sorry . . .’ He put his cheek against hers. ‘I’m so sorry. I don’t care what the Brotherhood says, I will burn for what I did to you.’

‘We nearly did burn.’ Her voice was soft by his ear – and then she coughed and pulled back.

‘Rosa?’ He clutched her, hardly able to believe she was alive, and she cried out, pulling her arm from his grip.

‘My arm!’ She held it up ruefully, looking at the weeping skin and broken blisters. ‘God, for a bit of magic to take the edge off . . .’

‘But – but you were cold!’

‘I am cold.’ She rubbed her hands and then touched his. ‘So are you.’ She shivered and then winced again. ‘Oh, my arm . . .’

‘Why can’t you heal it?’

‘I’m spent. Magic’s like . . . it’s like strength, in a way. If you asked me to lift that beam now, I doubt I could. My muscles are like wet wool. It’ll come back, but for now – I couldn’t conjure so much as a witchlight.’

She looked down at her scorched and blistered palm and Luke remembered the stable, the frail white glow in her hand . . .

‘You saved me,’ he said slowly. ‘I tried to kill you – and you saved me. Why? I deserve to burn for what I tried to do to you.’

‘You came back for me,’ she said simply.

For a long time they said nothing, just sat side by side in the ruins of Sebastian’s factory, looking out to the river and the boats drifting past. It was still early, the sky pale in the east, but Luke could hear the cries from the waterfront drifting downriver and he knew that the East End never really slept.

‘We must get going.’ He stood, painfully, feeling his exhausted muscles complaining and his stiff joints cracking. His hurt leg screamed as he stood, but it was not broken – just stiff and sprained. He put out a hand and Rosa scrambled to her feet and stood brushing down her charred silk gown with a rueful face. ‘Where will you go?’ he asked.

‘I don’t know.’

‘Well, we can’t stay here.’ Luke looked at the sky and then the river. ‘The police will come soon. And Knyvet will be back.’

Rosa shivered.

‘He has everything now: Southing, the factories, the Chair . . . But not me. And he would kill me for that, if he found out I was still alive. I cannot go home. Can we go back to your uncle’s? To the forge?’

‘No.’ Luke shook his head. ‘I told you, I was sent to kill you – the price for failing was death. My death.’

‘So, your people are as barbaric as mine,’ she said softly.

‘Not William,’ Luke said. He swallowed against the pain in his smoke-scorched throat. ‘William loves me. But I can’t – I can’t make him choose between me and the Brotherhood. I must go my own way, alone now.’

‘So must I.’ She took his hand and a faint prickle of magic, like a flame, lit her face for a moment, like a ray of warmth in this dreary fog-muted dawn. ‘So we are not alone.’

Luke nodded.

They turned, and together they began to walk towards the rising sun.