‘Luke Lexton!’ she cried. ‘Yes! That’s it, I made a mistake. I should have said Luke Lexton, not Welling. Do you know where he is?’

‘Made a mistake, didja?’ The girl snorted disbelievingly, but there was a smile at the corner of her mouth. ‘What do you want with Luke Lexton then? You’d need two more legs for him to take notice of you.’

‘What?’ Rosa said, too confused to be polite.

‘He’s sweeter on horses than women,’ Phoebe said. ‘Not that I wouldn’t give him a ride, if he came asking.’

Rosa knew she should pretend to be shocked, but she didn’t care.

‘Where does he live?’

‘At his uncle’s forge, off Farrer’s Lane. But his father’s no drayman – he’s dead.’

‘Farrer’s Lane – where’s that? Can you – would you show me?’

‘Why should I?’ The girl folded her arms and Rosa felt desperate. ‘I’m a working girl, darlin’. I get paid for my time.’

‘I don’t have any money!’ She could force Phoebe to tell her. That was dark magic, but she had seen the spells in the Grimoire, although Mama had told her never to look at those pages. If only she had a coin . . .

Phoebe looked her up and down appraisingly, her eyes hard. She seemed to come to a decision.

‘Give me that locket.’

‘What? No!’ Rosa’s hand closed around it reflexively. She felt its heavy warmth against her collarbone, where it had rested since Papa had given it to her on her tenth birthday. ‘You don’t understand . . .’

‘I understand that you want a service and you’re not prepared to pay for it. But I don’t care, wander the streets of Spitalfields on your own; you’ll soon find some kind fella prepared to take you under his wing, no doubt.’ She gave a raucous laugh and Rosa bit her lip. She could well imagine what kind of fellows she might meet in the dark streets between here and Luke’s uncle’s forge. They were spilling out of the Cock Tavern now, amorous and angry by turns. One of them plucked at Phoebe’s sleeve.

‘Gi’s a tumble, Phoebs, for old time’s sake, eh?’

‘Oh piss off, Nick Sykes, you old soak,’ the girl snarled. She gave him a shove and he stumbled backwards, tumbling into the filth-filled gutter where he lay, laughing or sobbing, Rosa could not tell which. Phoebe turned back to Rosa. ‘Well? Take it or leave it, I ain’t got the time to be gabbing here.’

‘I’ll take it,’ Rosa said, though her heart hurt as she fumbled for the catch of the locket. Phoebe reached for it, greedily, and Rosa said, ‘Wait!’

She opened it up and, using her nail, prised out the tiny pencil drawing of Papa. She saw now that it was crude, the work of a child. But it was all she had.

For a moment the locket hung from her fingers, still hers. Then she let it drop into Phoebe’s outstretched palm.

Phoebe nodded.

‘Come on then. Look slippy and don’t talk to no one. You’re like a fox in a hen house. No, hang about, that’s the wrong way round. But there ain’t no such thing as a fox house.’

But perhaps Phoebe had it right, Rosa thought, as she followed her down the first dark alleyway between two buildings. She was more dangerous, more predatory than any of the poor drunkards. She could gut them alive if she chose. She was aware, suddenly, horribly, of the power even the feeblest witch held over the outwith. No wonder their kind had been hated and feared for so long.

Phoebe was cheerful now, chatting as she led Rosa through stinking back alleys, where children played in spite of the filth and the darkness. They cut across the corner of a deserted market space, where a few beggars were rummaging in the cast-off boxes, and then up a street less forbidding than the rest, if only because it was emptier. The evening fog had begun to descend and Rosa shivered, wishing that she had not left her wrap in the carriage. What would the driver be thinking? Would Sebastian have noticed her absence?

Then suddenly Phoebe swung left through a low arch and into a cobbled yard. There was a roaring sound, as of a huge fire, coming from a low brick building to their right, and a shower of sparks flew up suddenly from the chimney.

‘Luke,’ Phoebe yelled. ‘Gotta visitor.’

‘Who is it?’ The voice was so familiar that Rosa choked. She could not speak.

Phoebe stuck her head through the door to the forge.

‘La-di-da type by the name of . . .’ She looked back over her shoulder at Rosa. ‘What was your name, darlin’?’

‘Rosa,’ she whispered. ‘Rosa Greenwood.’

‘Rosa Greenwood,’ Phoebe repeated back. There was a reply that Rosa could not hear and Phoebe shrugged and turned back to Rosa.

‘Says he’s never heard of you. Well, there you are. Not my fault if you made a mistake. Anyway, I’ve done what I said. Tarra now.’

And with a swish of skirts and a flash of scarlet petticoat, she was gone.

Rosa took a deep breath and stepped forward into the forge. For a minute she almost didn’t recognize the man working the bellows. He was stripped to the waist, sweating, his muscles standing out in the light from the fire, the flames flickering across his naked chest and shoulders. His head was down, his brows knit in effort or concentration.

Then he looked up and she saw his clear hazel eyes.

He wiped his brow with a cloth and then took a shirt from a peg by the door and pulled it over his head.

‘Yes, miss,’ he said as he tucked it in. His voice at least was familiar, the same low voice she remembered, though his East End accent sounded stronger than it had in Knightsbridge. ‘What can I do for you? My uncle’s not here, as you see.’

‘Luke . . .’ She didn’t know where to begin, how to start. ‘Luke, it’s me, Rosa.’

Something flickered in his eyes, not recognition, but a kind of wariness.

‘I’ve never seen you before,’ he said flatly.

‘That’s not true.’ What could she say? How could she convince him? She had taken everything, every memory of herself, of why he had come, of what had happened to him there. ‘I know things about you.’

‘Like what?’

‘I know that you’ve lost your memory, that you can’t remember anything for the last month back, maybe longer. I know that you have a scar on the back of your head, that you came back with a wound there, from a fight.’

‘Anyone could know that,’ he said hoarsely, though he looked uneasy. ‘You could have talked to Phoebe.’

‘I know that you have a mark on your shoulder.’ She thought of him washing under the pump in the yard. ‘A scar, like a brand.’

His hand went involuntarily to the place and then he shook his head.

‘You saw it while I was dressing, just now.’

‘Luke, why won’t you believe me?’ It was not what she wanted to ask; she wanted to shake him, ask why he’d come to Osborne House, why he had changed his name and lied about his father. Had it all been a lie? No – she thought of his confession, in the dark of the stable yard. His uncle and the forge – that had not been a lie. And she remembered his other confession. About what he could see.

‘I know something else,’ she whispered. ‘I know that you – that you . . .’ She swallowed. ‘I know that you can see witches.’

He flinched, as if she had slapped him.

‘It’s true, isn’t it?’

‘How do you know?’ he demanded. He was across the forge in an instant, grabbing her arms with a strength that almost frightened her, except that it was Luke, Luke who would never hurt her.

‘I know b-because . . . I am one.’

She let her magic shine out, feeling it flicker across her skin like electricity, flow through her limbs and her fingers, crackling to the tips of her hair like static energy.

Luke let go of her as if she had burnt him. He was staring at her with a look of horror. His hand went again to the scar on his shoulder as if it hurt.

Rosa stretched out her hands, where the witchlight burnt, clear and bright in her palm.

‘Please, Luke.’ She tried to reach him, to heal his mind, pour back the memories she had ripped out of him by the roots. ‘Don’t you remember? You came to my house, you saved my life, you kissed me.’

‘No!’ he cried desperately. He put his hands to his head, as if it might explode, as if something might crack. She was not sure if he was trying to force the memories back in, or keep them away.

‘It’s true. I need your help – I’ve found your friend Minna—’

‘Get out!’ He cut her off.

‘She’s at the match factory, down by the Thames, where I sent her, Luke. It’s horrible – the workers are under some kind of spell, they’re dying, but they won’t listen to me. Please, come and help—’

‘Get out!’ he roared. His face was suffused with blood.

‘Please, just—’

‘Help you?’ he cried. There was something desperate in his eyes, as if he was breaking apart inside. ‘How can I help you? I should kill you.’

‘What?’

‘Have you heard of the Malleus?’ He took a step towards her and for the first time she noticed that he had something in his hand. A hammer.

‘No,’ she whispered.

‘We’re sworn to kill your kind.’

‘No!’

‘Yes. Now, get out.’

Rosa looked at him. This is Luke, she told herself. She tried not to tremble. Luke!

He raised the hammer above his head.

She ran.

Luke watched as the girl disappeared into the fog. He could see the bright red-gold flame of her hair dwindling as she ran and then at last even that was gone, swallowed up in the darkness of the narrow streets.

He let the hammer fall from his hand on to the stone floor of the forge.

The Malleus. How could he have forgotten the Malleus?

Images flickered through his mind like half-forgotten dreams – the feel of the knife in his side, the screaming heat of the brand on his shoulder . . . His hand went to the mark beneath his shirt and now he knew what it meant. The hammer. The hammer of witches.

That girl – Rosa – he had never seen her before and yet he knew every inch of her face, the softness of her skin beneath his touch, the feel of her waist between his hands . . . How did he know her? Why?

And how did she know him?

He thought of her words: I know that you can see witches.

The scar at the back of his head gave a great throbbing pang and he vomited on to the floor, heaving and choking until there was nothing left but bile in his gut and he was cold and sweating, and full of fear.

What had he done?

Rosa ran. She ran without looking where she was going, turning at random in the narrow twisting streets, the fog parting and then closing behind her, enveloping her in its strange, muffled world. She stumbled past taverns disgorging drunks on to the pavement, past beggars crowded round braziers, past girls hawking watercress, their eyes huge in the darkness. At last she stopped in a quiet alleyway, panting, her lungs screaming for air, fighting against the constriction of her choking stays. There were black spots in front of her vision, dancing against the sickly yellow swirl of the fog, and she thought she might faint, but she did not. After a while her breathing began to slow and she tried to consider what to do next.

Luke was a killer?

It didn’t make sense.

And yet, in another horrible way, it did. It explained the way he had come so mysteriously with only Fred Welling’s word and no experience. It explained why he’d been prepared to fill in for no money. It explained – she shut her eyes as the realization washed over her – it explained the broken buckle. The buckle that she had taken responsibility for, when Alexis wanted him sacked.

She put her hands over her face.

He had tried to kill her.

He saved your life.

He had betrayed her.

He told you he loved you.

The voices crowded in her head, screaming at each other for domination.

Shut up – shut up! I can’t think!

She put her hand up to the locket to feel its reassuring weight in her palm as she tried to think what to do. But it was gone.

It began to rain, a fine mist of drizzle that mingled with the fog, clinging to her skin and hair in fine droplets. Rosa shivered.

The factory. Whatever had happened with Luke, it changed nothing about the factory, about the fact that she had sent an innocent girl there to her death. That was her wrong, not his. It was hers to undo.

Luke would not help her. There was no one left to turn to. It was down to her alone to sort this out. There were only two options: undo the charms herself, or force Sebastian to do it. But how?