Moll strained her eyes into the trees as they walked. Long, thin trunks wrapped in silver bark, they gave nothing away, no sign that anyone might be lurking between them. Their roots sprawled down to the path where woodrush and moss began, and beyond that the river roared, a dark churn beneath the moonlight. Moll watched as a salmon leapt upstream, its flimsy body nosing through the water. She closed her eyes for a moment and tried to read the wind’s spirit, like Cinderella Bull had taught her, but it sounded different here – hollow, like air blown through the top of a bottle. Every now and again, Gryff stopped, ears cocked, muscles taut, but the forest around them seemed empty. If there were witches here, they were keeping themselves hidden.

They walked on and on and the further along the path they went, the brighter the trees seemed to shine. Leaves sparkled like crystals against the darkness and, on the far side of the gorge, the birches looked as if they were coated in frost. Moll stretched out a hand and touched a leaf. It felt cool beneath her fingers – and stiff.

‘Sid,’ she said slowly. ‘The trees . . . they’re not ordinary birches. They’re not even made of wood. They’re silver.’

Siddy ran his palm down a trunk and gasped. Moll was right. The bark was cold and hard, like a marble pillar. ‘That’s why the wind sounds different here,’ he murmured. ‘Because it’s slipping between metal not leaves . . .’

Moll adjusted the quiver on her back. The forest was beautiful – like a world frozen by moonlight – but trees made of silver meant there was an enchantment involved and if the witches were near it was bound to mean dark magic.

Moll dropped her voice until it was barely a whisper. ‘Keep your eyes open, Sid. The witches could be close.’

They walked over a bridge covered in lichen that crossed a stream leading down to the river and, though Moll tried to focus her mind on the dangers that could be hiding in the Clattering Gorge, she found herself thinking of Alfie. Where had he gone when the Soul Splinter shattered? Down into the Underworld, forever a prisoner of the dark magic? Or was he here, somewhere in her world? Something inside Moll, perhaps just the feeling deep in her gut that Domino had spoken of back in the forest, made her feel as if Alfie was still here – that somewhere his heart was still beating and his thoughts were turning – but would finding the amulet mean undoing all the curses the Shadowmasks had conjured? Would it mean bringing Alfie back to life as someone who could be seen by everyone, not just by those who believed in the Bone Murmur?

Moll tried to hold her friend’s face up in her mind, tried to remember his blue eyes and scruffy fair hair, his jay feather earring and old leather boots, but with each day that passed the image seemed to fade and with it a rising sense of panic trembled inside Moll.

‘Look at those nests!’ Siddy murmured as they stepped off the bridge back on to the path. ‘They’re huge . . .’

Moll pulled herself free from her thoughts and glanced up to where Siddy was pointing. Within the branches of the birch trees were large bundles of sticks. Like the rest of the forest they were silver, but they were bigger than any nest Moll had ever seen – bigger than a crow’s or a buzzard’s, bigger even than an eagle’s eyrie.

‘What kind of bird would live in a nest like that?’ Moll asked.

Siddy shivered. ‘I’m not sure I want to find out. Let’s keep walking.’

The path wound on beside the gorge and, at first, Moll thought it was just the wind that she could hear, rustling through the metal trees. But, when Gryff stopped and growled, she strained her ears past the roar of water and the thudding of her heart, and then she heard it too. There was another sound in the forest, one not made by the river or the wind or the trees.

Moll grabbed Siddy’s arm. ‘Listen.’

They stood still on the path and, after a moment, they heard it more clearly. Music. Chords that started low and soft, like wind sighing in the hollows of a valley, then they faded and in their place notes rippled and slid.

Siddy bit his lip. ‘Is that the witches’ song?’

‘It must be. But,’ Moll’s eyes flitted between the birch trunks, ‘I can’t see anyone.’

The music swelled and softened around them and with every note Moll felt a strange sleepiness close in, a fog inside her mind that seemed to swallow all her thoughts. She shook her head, remembering Angus’ words about the family who had been lulled by the witches’ music and then taken.

‘Don’t listen to the music, Sid.’ Moll raised her hands to cover her ears. ‘Keep walking and be ready to grab your bow.’

Moll concentrated hard on her impossible dream, on the only thought powerful enough to unlock the Oracle Spirit inside her arrows. To make Alfie real, that was her dream, and Moll knew she’d need to believe in it with every fibre in her body to bring the Shadowmasks’ magic down.

Gryff stopped abruptly, his tail low to the ground. He’d seen something. Moll lifted her bow from her shoulder and, trying to ignore the music, she fitted an arrow to the string and looked into the trees. Set back from the path, beyond a cluster of birches laden with large silver nests, was a folly, a half-ruined temple of stones entwined with ivy. There were walls still, and long, rectangular holes where windows might once have been, but the roof had long since fallen in. The music was louder here – a crystal-clear melody that reminded Moll of water trickling – and it whispered to her that there was nothing to fear. She blinked again and again to keep herself awake and beside her Siddy yawned and even Gryff moved slowly, almost clumsily, through the trees.

‘We’ve got to follow this music,’ Moll said firmly, ‘without getting trapped under its spell. And then we need to . . .’ Her voice trailed off.

‘Steal it,’ Siddy finished for her.

It sounded ridiculous out loud – impossible even – but they had to try. Gryff shook himself, then prowled into the bracken and, with their bows raised, Moll and Siddy followed.

The music grew louder, throbbing in their ears and rolling through the silver birches. Every note seemed to soothe Moll’s nerves and more than once she found herself yawning, but she swallowed the tiredness and pressed on between the trees until they were all outside the folly together, crouched beneath a window.

With an arrow still set to her bow, Moll lifted her head above the stonework. There were no witches huddled inside, singing; there were no people at all. Instead, in the middle of the folly, there was a grand piano with its lid propped open. Nettles grew around it, ivy twisted up the legs and moss clung to the strings splayed out under the lid. But the strangest thing about this piano was that the instrument was playing by itself.

Siddy peered over Moll’s shoulder, his eyes wide. ‘Where are the witches?’

‘I don’t know,’ Moll whispered.

But she knew enough of dark magic to realise that just because the witches couldn’t be seen didn’t mean that they weren’t there. The two children watched the piano notes rise and fall.

‘How do we steal their song if they’re not even here?’ Siddy hissed. ‘We can’t just make off with a piano!’

Gryff growled behind them, a low, throaty sound that rose with the fur on his back. Moll and Siddy whirled round and the music grew louder and more discordant, the notes jarring and clashing before rising into a hideous roar that stamped out Moll, Sid and Gryff’s drowsiness in an instant. But then, from the nests in the trees around them, shapes began to stir. Orange talons curled over the sticks and feathered legs crawled out, long and thin and black.

‘B – birds?’ Siddy stammered.

Dark hair followed the legs, spilling all the way down to the ground, and then female faces appeared, together with more talons where hands should have been, and porcelain skin with lips as red as rowan berries.

‘Witches,’ Moll breathed and her body tightened with fear.