Flint raced across the Driftlands on a sled pulled by huskies. The dogs strained against their harnesses as they bounded forward, but they did not yap or bark. They ran silently, as if they could sense the boy’s fear, and only the runners skimming the tundra could be heard.

Standing upright at the back of the sled, his boots astride on the caribou antlers and his scruff of brown hair flapping about his face, Flint used the moonlight to guide him. Round hillocks of ice, down dips in the snowfall, on and on towards Winterfang Palace. It was a cold night and Flint’s breath froze in little crystals on the lynx-fur trim of his parka. But, despite the chill, he didn’t have his hood pulled up because that would have meant dislodging the fox pup snuggled inside.

‘Look, Pebble,’ Flint whispered. ‘It’s Winterfang. There’s no turning back now . . .’

There was a shuffle of white fur from inside Flint’s hood, then two black eyes emerged. Pebble blinked. They were rushing along the coast now and to their right the snowy cliffs plunged down to the sea. In a few weeks, they’d see beluga whales gliding between icebergs and walruses resting on the shores, but for now the sea was still mostly frozen and, further up the coast, a jumble of domes and towers burst out of the Ice Queen’s enchanted iceberg.

Pebble nibbled at Flint’s bear-claw earring. The fox pup was used to the trespassing, mishaps and tellings-off that came with belonging to Flint, but he was always well fed throughout each ordeal which meant the ongoing peril was usually worth the trouble.

Flint tapped Pebble’s nose. ‘Now is not the time to be asking for extra food. We’ve got a handful of Tusk guards to get past, a palace to break into and my ma to free.’ He paused. Put like that, the evening sounded rather intense, but then he thought about the items stashed inside his rucksack and the months he’d spent planning in his tree house and he felt his courage return. ‘Besides,’ he continued, ‘I fed you back at Deeproots and you had seconds of lemmings, if I remember correctly.’

Pebble grunted, then turned round and stuck out his bushy tail until it was smothering Flint’s face. Flint pushed it away and reluctantly Pebble got the message and manoeuvred his bottom back inside the hood. They sped on.

‘The guards will be celebrating long into the night – just like they did last year when the first sun rose after winter.’ Flint paused as the sled bumped over a shelf of ice. ‘If ever there was a moment to sneak into the palace, it’s tonight, when they’re distracted.’

But, despite the nights Flint had spent spying on the palace and preparing for the break-in, there was a tremble in his voice and his eyes flitted with nerves – because Flint knew the stories of the Ice Queen as well as anyone else. She could kill a person just by holding up her staff, or so people said, and no one hiding in Deeproots Forest or the Never Cliffs could miss the sounds that drifted out from Winterfang every morning: the Ice Queen’s organ first, then the haunting chorus of voices – the mothers, fathers, uncles, aunts and grandparents of the hidden children – locked inside the palace. They could drive you mad, those voices, and now anyone who heard them raised their hands to cover their ears.

The sled raced on and the palace drew nearer. Flint swallowed as he took in the jungle of gigantic icicles surrounding the base of each of the five towers rumoured to hold the Ice Queen’s prisoners. They cast a web of sprawling shadows over the moonlit tundra and for a moment Flint’s mittens slackened their grip on the sled. He thought about his ma, trapped inside, and focused on the main palace wall. He’d climb in that way, then sneak through the passageways to the towers from there.

Flint reached back and tickled Pebble’s chin as the dogs approached a bank of snow that blocked the palace from sight. ‘Tomkin might have shouted down my talk of a rescue mission because he doesn’t think I’m ready to be a proper warrior or that my inventions are up to the job. But, when I return to Deeproots with Ma, my brother will soon see what I’m capable of.’

Flint wasn’t proud of the fact that he’d lied to his brother. He’d promised Tomkin he’d destroyed all of his inventions back in his tree house because as Tomkin always said: ‘A Fur Tribe warrior fights with spears and fists, not with magic and far-fetched contraptions’ – but the truth was, Flint couldn’t shut his thoughts away. Ever since he was a little boy, he’d been inventing things and now, no matter how hard he tried to stop his ideas, they kept happening, kept growing, kept changing into extraordinary possibilities. Because, unlike his brother and everyone else in his tribe, Flint still trusted Erkenwald’s magic. This was partly because of the piece of bark he’d found in the forest over the summer which bore carvings that talked of how to harness magic and use it for good. But also because his mind was attuned to the things most people missed – river stones that shone in the dark, sunbeams tucked behind trees, coils of mist hovering above puddles.

Flint was sure that, if handled correctly, Erkenwald’s magic could be stronger than a warrior’s spear.

He steered his sled into a hollow in the bank that spread out into a hidden passageway winding down to the sea. The dogs raced into the darkness until eventually the ground levelled out into an ice cavern and moonlight sparkled against the icicles fringing the way out. Flint tethered the panting animals and placed a finger to his lips.

‘I’ll be back soon,’ he told the dogs as he swung his rucksack on to his shoulder. ‘Probably.’

One of the dogs whined and Flint reached into a bag on the sled and pulled out the frozen rabbit meat inside. He tossed it to the dogs and they chewed hungrily.

Then, with Pebble peeping out from his hood, Flint turned from the cavern and crept towards the palace. The fortress glinted in the moonlight and as Flint slipped beneath the bridge that connected the iceberg to the cliff top on the mainland – his sealskin boots practically soundless against the ice – he realised he had been holding his breath for almost a minute. He breathed out.

Immediately, his body stiffened.

Voices.

A cluster of Tusk guards were chattering on the bridge above him and, as Flint listened, he heard mugs clinking together and a fire crackling. He didn’t need to look to know they’d be clad in the armour the Ice Queen had sculpted for them – breastplates of ice and helmets forked with walrus tusks. Heart skittering, Flint stole on, using the shadow of the bridge to hide him.

He paused at the foot of the palace to strap a pair of crampons to his boots, then he swallowed as he took in the glinting base of ice that he needed to climb before he got to the arches opening up into Winterfang. Pebble shivered behind him. They would be in full view of the guards on that ice face, an easy target for one of their spears, but Flint had thought this through. He knew exactly what was needed to create a diversion.

He lifted a whistle carved from gyrfalcon bone out of his rucksack and checked for the handful of snowy owl feathers wedged inside it. He breathed a sigh of relief. The feathers were still there, and that was just as well, because his whole invention hinged on them. Gathered under a full moon out on the tundra, then dipped in rainwater collected before it touched the ground, the feathers had magical properties, if Erkenwald’s magic was to be believed.

Flint clasped the whistle and blew. No sound came out – the feathers muffled it – but eventually they eased out of the whistle and fluttered silently into the sky. Pebble’s eyes grew large and Flint bit his lip as they watched the feathers float eerily above the bridge and trail quite some distance across the tundra. Then, when the feathers were a long way away, Flint’s whistle sounded.

The guards leapt up and began shouting. Flint grinned. His invention had worked. The feathers had carried the sound of his whistle, only releasing the blast when it was a safe enough distance from him. The Tusks rushed down the bridge and away from the palace towards the noise while Flint hauled a bundle of rope from his rucksack. This was the diversion he’d wanted, but he would have to be quick.

He hurled the end of the rope tipped with a barbed hook up against the ice and it held fast, then he tightened the drawstring around his hood to secure Pebble in place, set his crampons to the wall and climbed up towards the arches. Once or twice his boots skidded down the ice, but Flint kept on going, every now and again throwing a glance behind him to check that the guards were still out on the tundra.

Eventually, Flint came to the arches. He crouched just below them, panting, and Pebble gave a little moan as he peered over the edge of Flint’s hood. They were closer to the palace than they’d ever been, just moments away from breaking in, and as Flint thought of his ma and all the nights he’d spent missing her in the forest he hoisted himself up into the arch.

And froze.

There was a face looking up at him, but it did not boast a crown of snowflakes which the Ice Queen was rumoured to wear. This face belonged to a thin pale girl hunched on a pedestal – and it held eyes full of longing.

‘Help me.’ The girl’s voice was a scratched whisper, as if she hadn’t used it in a long, long time. ‘You have to help me.’