Gryff tugged at Moll’s coat sleeve and she opened one eye.

‘Brrroooooo.’

She let the wildcat’s greeting call rumble in her ears, then she sat up and yawned. Siddy was lying beside her, snoring, with Frank curled up on his chest and, at the far end of the raft, Bruce was peering out through the cocoon. Moll followed his upward gaze. Brown-flecked feathers rippled in the wind and far below the ospreys the sea sprawled out towards an unknown horizon. Sunlight bobbed on the waves and it was so warm and snug inside the cocoon that it might have been a summer’s day had the coastline to their right not told another story. White mountains rose up from the sea, their bases ringed with ice, and wisps of snow unfurled from the peaks.

Frank stirred from Siddy’s chest and, on seeing Moll and Gryff awake, nibbled on Siddy’s ear.

‘The mountains,’ Siddy murmured, rubbing his eyes as he looked out of the cocoon. ‘They go on forever.’

Moll nodded. For as far as they could see, peaks and ridges jutted across the land. They were colossal, like the bone structure of a mighty dragon, and they reached such dizzying heights it looked as if they were propping up the sky itself. Moll swallowed. Somehow they had to find the last amulet among them tonight . . .

There was a sharp cry from above and suddenly the ospreys tucked in their wings, the raft swung to one side and the birds bulleted towards the sea.

‘Hold on!’ Moll yelled, clutching Gryff with one hand and digging her nails into the raft with the other.

Her stomach swung to her throat and her eyes streamed as the birds plunged down, down, down – then the raft hit the water with a jolt, the silk around them hardened into a glass-like cocoon again, and once more they felt the familiar push and pull of the tide around them. Using their beaks, the ospreys nudged the raft up to the base of the nearest mountain before launching into the sky and gliding away over the mountains. But, where the ospreys had been on the ledges of rock, there was now a person: a woman whose face told of magic and undiscovered worlds.

‘Is – is that . . .?’ Moll’s voice trailed off in disbelief.

The messenger from the Otherworld was exactly as Moll remembered her: blue swishes of colour looped from her cheekbones up over her brow, pale green dots curved beneath her eyes and a long silver plait hung down over her dress. The only change was the fur cape she wore which curled round her body like folds of fresh snow.

Siddy pressed his palms up against the cocoon. ‘Willow!’

The woman dipped her head towards them and something in the gesture reminded Moll of how Gryff greeted her after time apart. Willow took a deep breath and as she exhaled, the cocoon around them faded and then vanished. Moll shivered at the sudden chill of air.

‘I do not have long,’ Willow said. Her voice was quieter than it had been in the forest when they’d first met. It was almost a whisper, like a trail of words carried loosely on the wind, and now that Moll looked more closely Willow’s body looked different too – faded at the edges as if the Oracle Spirit was only just in Moll’s world. ‘The dark magic is trying to hold me back even now,’ Willow continued. ‘But, when you destroyed Orbrot, the Shadowmasks’ power weakened for a moment and I was able to find a way through to you.’ The markings around her eyes tightened. ‘Keep hold of your bow, Moll.’

Moll frowned. ‘But I lost the last of my arrows and—’

Willow cut through her words. ‘Keep the bow and follow the selkie.’

She leapt from the rock out on to the raft and Moll and Siddy held their breath at the sight of magic so close and so full of urgency. Willow leant forward and touched the whistle hanging around Moll’s neck and Moll gasped as she watched the Oracle Spirit’s touch transform it into a small key carved from bone. Engravings ran down each side.

‘Oracle Bone script,’ Moll murmured, turning it over in her palm.

Willow nodded. ‘Magic does not fix as one thing for very long. You only need to blink or turn away and it disappears, but it is never gone for good. Look after that key, Moll. You will know when to use it.’ She drew herself up, her body fading in the sunlight before them. ‘I must leave you now – the Night Spinner’s dark magic isn’t far behind – but we will meet again. That much I know. When you have found what lies one hundred years deep, head north on foot. Over the Barbed Peaks.’ She paused. ‘And know, as ever, that the old magic is willing you on every step of the way.’

She twisted her hands above her head, as if running them over invisible objects, and then, from Willow’s fingertips, silver shapes swirled into the air, like wisps of smoke, and as they drifted slowly down to the raft they hardened into objects the group couldn’t have been happier to see: goblets full of steaming hot chocolate, bowls of warm milk for Gryff and Frank, fresh fish for Bruce and trays laden with porridge, fresh fruit and buttered toast. But where Willow had been there was nothing – just the feel of magic glimpsed and then lost.

Siddy glanced around. ‘Do you think we have time to eat it? The Night Spinner could be here any moment.’

Moll considered. ‘I think it’s important to eat breakfast before tackling dark magic; Willow wouldn’t have conjured it all up otherwise.’

Siddy picked up a goblet. ‘I agree.’

They ate hungrily, scraping at the bowls of porridge and draining the hot chocolate in glugs, and, when they had finished, the mysterious feast vanished, just as Willow had done.

Moll watched the sea for a moment, ruffled by the morning breeze, then, as Bruce slipped back into the water, she and Siddy dug their oars into the waves and followed the selkie as he swam further up the coast. Hours drifted by with Gryff and Frank keeping watch at both ends of the raft again and, though Moll’s hands were blistered inside her gloves, she kept on paddling – always north – with the cries of the kittiwakes in her ears.

Eventually Bruce slowed. They had approached a gap between the cliffs and, as the raft edged closer to it, Moll and Siddy realised it was in fact a fjord cutting inland to form a giant loch. Bruce stopped and as Moll looked at the slice of water within the mountains she saw that it was frighteningly still, like glass, washed white by the reflection of snow from the cliffs either side. The selkie’s nose twitched, but he did not go any further. Instead, he hovered before the loch as if it was something important but also something to fear.

‘Bruce has come to the end of his journey,’ Moll said, slowly understanding.

Siddy nodded. ‘And I have a feeling ours is only just beginning.’ His eyes travelled the length of the loch. ‘One hundred years deep. Why do I have a feeling that whatever we want is down at the bottom?’

Bruce swam up to the raft and placed a flipper on the wood and Siddy and Moll crouched before him.

‘You were very clever back at Greystone,’ Moll said.

Siddy nodded. ‘And very brave with the kraken.’

Bruce croaked and then to Moll’s surprise Gryff prowled close, dipping his head before the seal pup. Feeling left out, Frank joined the group and did a little leg kick before the selkie, and Moll smiled. Her and Siddy’s journey had been fraught with peril, but it had also been full of unexpected friends, of people they’d grown to love and trust and without whom they would never have made it this far.

‘We won’t forget you, Bruce,’ Moll said quietly.

Siddy nodded. ‘Back in our camp we tell stories around the fire and, when all this is over, when me and Moll are back with our family and friends, we’re going to tell your story.’

Moll stroked the seal pup’s head. ‘And it’ll be the finest story anyone has ever told.’

Bruce placed his flipper over both Moll and Siddy’s hands and then he croaked again before sinking beneath the water to make his long journey home.

Moll and Siddy squinted into the mid-morning sun as they looked out across the loch.

‘Don’t even ask if I have a plan for how we get the amulet,’ Moll said, ‘because I don’t.’ She shuffled closer to Gryff as she thought of an endless deep falling away beneath their raft, then she glanced at the two dark-haired shapes bobbing up by a rock further out in the ocean.

‘Sea otters,’ Siddy said, following her gaze. ‘Back in Little Hollows, Oak told me that they hold hands when they sleep so that they don’t float away from each other.’

Moll looked at the great white stillness in front of them, then she reached out and squeezed Siddy’s hand. He squeezed back, and then together they picked up their oars and steered the raft into the cliffs.

Moll took in the mountains either side of them, great shields of snow that climbed vertically upwards into dizzying heights, boxing them in on all sides and blocking out the morning sun. There were no gulls bobbing on the water, no fish nosing the surface. This was a place of stillness and silence.

They paddled on, Gryff pressed close to Moll’s side and Frank perched on Siddy’s knee, until Moll pointed to a wooden jetty leading out from the base of the cliff at the far end of the loch. There was a small shingle beach there and what looked like an old fishing hut.

‘Let’s make for that,’ Moll said. ‘I think we should get off the water.’

Finally, they came to the jetty and, using the piano string to tie the raft to a mooring ring there, they hoisted themselves up and sat on the dock, legs tucked up under their chins and heads down to fight the cold.

‘We’re at a dead end, aren’t we?’ Siddy mumbled. ‘How can we get down to the bottom of this loch without freezing – or without breathing – before the Night Spinner finds us?’

Moll watched as Frank hurried up and down the piano string that moored the raft, then she turned to Siddy. ‘Willow’s letter said: steal the last note of the witches’ song then take a feather from burning wings and you’ll find what you need one hundred years deep. Maybe we need to use the things we’ve found to get the amulet,’ Moll said. ‘The piano string is endless and even though it’s almost invisible there’s a weight to it, so we could use it like a fishing line to reach the bottom.’ She paused. ‘We know the string’s magical so maybe it’ll have the power to tie itself round the amulet and haul it up for us.’

Siddy nodded, then he looked out across the water. ‘This loch is huge and we don’t even know what we’re looking for. It could be anywhere . . .’

But Gryff and Frank were already down on the raft again, clawing the string away from the driftwood.

‘They’re unpicking it,’ Siddy said slowly.

Moll nodded. ‘They’re right. We don’t need the raft any more – Willow told us to go on by foot.’ She glanced at Gryff who had managed to loosen the first log. ‘Come on, let’s help them – we need to move fast.’

When there were just a few planks left, they jumped back up on to the jetty and Moll wound in the last of the string. She clutched the reel in her gloves and then little by little she let it out again, dropping it slowly through the water. It lengthened before their eyes, a silvery thread glistening in the splice of sunlight that edged over the cliffs, before sinking into the milky water. Down and down it went as Moll unravelled it through her fingers, but, after ten minutes, she slid a nervous glance to Siddy.

‘What if we never reach the bottom?’

‘Keep going,’ Siddy said firmly. ‘It’s our only hope.’

Moll loosed more and more of the piano string and then, across the great silence of the loch, music started. It wasn’t like the haunting melody in the Clattering Gorge. This was different: a single, low note that thrummed between the cliffs as if it might be summoning someone or something from very far away. Moll gripped the piano string tightly so that it couldn’t unravel any more and instantly the music stopped.

Siddy’s shoulders hunched and Frank tiptoed back inside his coat pocket. ‘You may not have hit the bottom, but you’ve disturbed something . . .’

Moll’s eyes glazed with dread. ‘Not witches again?’

Siddy shook his head. ‘I don’t think so. This feels different somehow.’

Moll nodded, then Gryff nudged her arm and, with shaking hands, she released more of the string into the loch. Again the note sounded, rich and low and filled with foreboding. Moll jumped.

‘What is it?’ Siddy cried.

‘There’s something on the end of the string.’ Moll peered over the edge of the jetty. ‘I can feel it – a weight tugging hard.’

‘Do you think it’s the amulet?’ Siddy asked hopefully.

Moll kept pulling and then ripples started spilling out around the string and Siddy huddled close. The ripples quickened, the piano note swelled and then it cut to silence as a webbed hand burst out of the water.

‘It’s a monster!’ Siddy screamed. ‘And we’ve gone and woken it up!’