They emerged from the fishing hut into a world dusted white. The jetty was a plank of snow and Moll and Siddy tensed as they glimpsed the loch, now covered in great sheets of ice that creaked and groaned into the silent fjord.

‘This is no ordinary weather,’ Murk muttered as still more snow fell.

Moll nodded. ‘This is the Night Spinner’s doing. My friend Aira from the Highland Watch told me the dark magic has conjured the worst mists and snows the north has ever seen.’

They walked across the pebbled shore until they were standing at the foot of the Stone Necklace.

‘See?’ Murk said glumly. ‘It’s too big. Far too big.’

Moll let her eyes travel from its base right up to the jagged ridge. It was a giant wall of rock, covered in snow and polished, in parts, with ice. She blinked as the snowflakes sprinkled down, peeling from the peaks in shifting ribbons.

‘Enormous. Colossal. Gargantuan,’ Murk mumbled. ‘Never seen anything the size of the Stone Necklace.’

Moll turned to the old woman. ‘I thought once the arrow was out you’d cheer up.’

Murk shook her head. ‘It’s in a loch monster’s nature to be gloomy. And what I see in front of me is the gloomiest of things yet.’

Siddy rolled his eyes and from his pocket Frank stuck out a little pink tongue at the loch monster.

Moll tugged her cap down over her ears. ‘Right,’ she muttered. ‘Let’s get climbing.’

Murk nodded. ‘Terrible idea but yes, off you go. And good luck! Though it probably won’t help.’

‘Goodbye, Murk,’ Siddy said. ‘I hope you enjoy the depths of the loch now.’

Murk nodded. ‘It’ll be splendid. Unless the selkies crowd in and bother me. Or the ice covers my surfacing spots. Or everyone forgets I exist and no one comes to visit me for another one hundred years. Goodbye!’

The old woman waved from the shore, a resigned grimace plastered on her face, as Moll, Siddy, Gryff and Frank walked to the base of the Stone Necklace. Gryff set off first, his claws gripping fast on the rocks beneath the snow, but, when Moll and Siddy tried to follow, their boots slid on the icy crags, their gloves scrabbled for holds and they tumbled back to the shore.

Murk called after them. ‘See what I mean? Completely hopeless, as I said. Might as well just sit and wait for the Shadowmask to have his wicked way . . .’

Moll watched the wildcat springing between ledges of snow, up to places where she couldn’t follow, then she threw herself at the cliff face again. But, when she landed, with a thump, at Siddy’s feet, he shook his head.

‘It’s not going to work. We need something to hold on to as we climb.’ Siddy glanced at Moll’s pocket. ‘I think I’ve got an idea.’

A short while later, Moll was pulling back on her bow, the silver arrow taut against it, and a knot of piano string wound round its tip that then trailed into Siddy’s hands.

‘Aim for the highest point you can, Moll,’ Siddy said. ‘And fire hard so that it sticks into a crag.’

From behind them, Murk let out a strangled wail, then covered her eyes with her webbed hands. ‘Oh, I can’t watch. It’s too awful.’

But Moll wasn’t listening any more because poised some way up the cliff was Gryff, and he was waiting for them to follow. She watched him for a moment and then her gaze flicked upwards, to the highest point of the cliff, and closing one eye, she drew the arrow back against her chin, and fired hard.

The arrow shot upwards, the string in Siddy’s hands materialising out of thin air and unravelling as it went. A glint of silver racing through the snow, the arrow soared up and up and up the Stone Necklace until it struck the cliff top and dug hard into a crag.

Siddy grinned and Murk peeped out between her fingers and raised her eyebrows in surprise. ‘Well done! But you’ll probably break your legs on the next bit.’

Moll grabbed hold of the piano string, visible only because of the flakes of snow which landed on it. She tugged hard and knew that it would take her, Siddy and Frank’s weight – because the old magic was something they could rely on, even in the face of a towering mountain.

She set her boots against the cliff, looked up at the peaks, almost lost in the swirl of snow, and began to climb after Gryff, her gloves wrapped tightly round the piano string. And, though her toes and fingers were numb and snowflakes smudged on to her eyelashes, she kept on climbing – over ledges and overhangs, across chasms and crevasses – feeling Siddy and Frank behind her in the way the piano string moved. Once or twice, her boots skidded on the ice and she stumbled several metres down, but every time the string held fast and Moll carried on going.

The summit came almost as a surprise. The sky was white and full of snow and, set against the Stone Necklace, the two things were hard to tell apart. But Gryff was there, nuzzling against Moll’s side as she threw her body on to the top. The wind was wilder here and as Moll took in the view ahead she gulped. The mighty ridge that was the Stone Necklace curved round from the sea far inland, but spread out in front of her, for as far as her eyes could reach through the falling snow, were mountains – vast peaks with plunging sides and crests that scored the horizon. Frozen waterfalls had been sculpted over some crags while others were a haunting maze of snow and rock and ice.

Moll shivered. ‘Somewhere out there is the last Shadowmask.’

Siddy clambered up on to the ridge beside her, his cheeks red from the cold and the climb. He collapsed in the snow. ‘We did it!’

Frank leapt excitedly from Siddy’s coat, but promptly sank into the snow and had to be picked back up and pocketed. Then Moll, Siddy and Gryff peered back over the cliff edge. They could just make out a dark dot on the shoreline.

‘What do you think Murk would say if she was up here with us now?’ Siddy asked.

‘That if we don’t break our necks in the Barbed Peaks the last Shadowmask will come and break them for us.’

Siddy nodded. ‘Probably.’

They watched as the dot shuffled out across the ice and then sank through a hole and disappeared into the loch. Then they turned back to the Barbed Peaks and, through the screen of snow, they watched a covey of ptarmigan pour over a ridge and then drop down into a hollow. Moll yanked the arrow from the crag and tucked the string into her pocket, then she took a deep breath.

‘We stay together out here in the mountains – all of us. You, me and Gryff.’

‘And Frank,’ Siddy added as the ferret raised a defiant chin towards Moll.

Gryff led the way on to a ridge that wound out from the Stone Necklace. The snow gusted around them and lay thick about their boots, but they plodded north, as Willow had told them, following the highest points of the mountains to avoid the snowdrifts gathering in the folds. Some of the ridges were so narrow they had to go single file, edging round crags and leaping over drops, but they trudged on and little by little they made their way through the Barbed Peaks.

Somewhere behind the papery skies was the fading sun, but, even if it had been able to push through the clouds, they didn’t have long before darkness fell. The sky was turning – a backlit blue spliced with orange – and soon the moon would be riding high and the last Shadowmask would be just hours away from casting his eternal night. Moll shuddered inside her coat. They didn’t even know where they were heading and yet they were the ones tasked with halting this everlasting darkness.

Moll blinked as a hare skimmed the ridge, its amber eyes glinting against the sifting snow, then Gryff stopped on a rocky crag. His ears swivelled, his whiskers twitched and then he grunted and kept on walking. Moll chewed her lip as she tried to work out some sort of plan, but, moments later, Gryff stopped again, pausing mid-stride before scrambling backwards into Moll’s legs. Moll felt the wildcat’s heartbeat clamour against her legs. Something wasn’t right.

‘What is it?’ Moll whispered, crouching beside Gryff.

The wildcat’s ears were flattened to his head, then he growled and began to run back the way they’d come.

Siddy strained his eyes towards the next peak and Frank’s head darted this way and that from his pocket. ‘But – there’s nothing there!’

Moll grabbed his arm and yanked him back. ‘I don’t care! Gryff’s never wrong!’

They hurtled back up the pass, their boots skidding through the snow and scree, but, before they reached the peak, the whole mountain beneath them began to shake. Gently at first, like a tremor from a distant earthquake, and then stronger so that the force was enough to knock Moll and Siddy to their knees. They clung on to the crags with Gryff and Frank and the snow whirled around them.

‘An earthquake?’ Moll shouted.

But, as the entire mountain shook itself free from the ground and reared up into the air, Moll realised that this wasn’t an earthquake and they weren’t clinging to an ordinary crag. They were hanging from a leg and that leg belonged to an enormous man built from the rock itself.

The blood pounded in Moll’s temples as she remembered Aira’s words.

In among the Barbed Peaks, there were giants.