The orcas pushed the iceberg on, but when they came to the blue ice tunnel again they left, as soundlessly as they had arrived, and Eska’s head filled with images of what she had last seen there: Flint urging her to go on to the last of the Groaning Splinters; Blu’s terrified face as the walrus thrashed close; the sea swaying red. Fresh tears bloomed and for a moment Eska felt so numb and empty she couldn’t move, then Balapan leant close to her and she took a deep breath, laid the Frost Horn by her feet and paddled back between the remaining icebergs into the open water.

The midday sun was dazzling, but through its glare she could just make out the igloo back on the snowy beach. She didn’t have a plan yet, but she hadn’t heard her voice echo out over the kingdom so maybe, just maybe, there was still time for an idea to work itself out. But blowing the Frost Horn from the stars? She wasn’t an inventor, like Flint, so how was she going to climb up into the sky? A tear trailed down her cheek as she thought of Flint and Blu, and then her heart quickened. Back on the beach, through the haze of sunlight, something was moving.

She squinted. Not possible, a voice inside her whispered. And then, Please let it be possible . . .

She dug her bow into the water again and again, pushing through the stream of sunlight until she burst through – and there, on the beach, were two people. A little girl dressed in furs playing with a fox pup on the rocks near the end of the bay and a boy with a mop of tangled brown hair disappearing inside the igloo.

They were alive! Somehow Blu and Flint had survived the walrus attack and were waiting for her to return with the Frost Horn. Eska flung up her arms to get their attention – then, out of the corner of her eye, she saw something else.

A skin-boat was rounding the headland into their bay, a Tusk guard at its helm, and he was just a few metres from the rocks where Blu was cuddling Pebble.

Eska opened her mouth to shout out, suddenly forgetting her voice had been stolen, and when no sound came she threw up her hands. But Blu was facing the wrong way – she couldn’t see Eska or the Tusk guard approaching. Mind whirring, Eska seized the Frost Horn and blew as hard as she could. Nothing happened. Would the horn only sound if blown from the stars?

Balapan pecked at her furs. Stay low, the eagle was saying. Stay hidden. Don’t do anything that might draw attention.

Eska steered behind a solitary iceberg, then she peeped round to scan the beach for Flint. He was inside the igloo still and, as the Tusk guard silently pulled up his boat and edged over the rocks towards Blu, Eska’s body stiffened with fear. She was defenceless. No match for the guard and the weapons she saw glinting in his boat.

She made to move – anything to try and warn Blu – but then she realised that if the guard saw her, too, he’d raise the alarm and there could be more Tusks further up the coast. They’d take them both, then they’d destroy the Frost Horn and there would be no hope of beating the Ice Queen.

Eska watched in horror as Pebble launched himself at the Tusk guard to try and protect Blu, but he was booted into the snow as the guard clamped a hand over Blu’s mouth. Pebble struggled up and ran at the guard again, but the man simply seized the fox pup by the snout and dragged both him and Blu towards his skin-boat before binding and gagging them.

The guard began to row back round the headland, not thinking to check inside the igloo. And, though Balapan was pressing all her weight against Eska, trying to hold her back, Eska couldn’t just watch as Blu and Pebble were led away. She steered the iceberg into the open and stood up, shouting empty words and waving her hands. Blu’s eyes met hers, wide and scared, but the Tusk guard was facing the other way, rowing hard along the coast in the direction of the Ice Queen’s palace.

Confident now that the guard hadn’t seen Eska, Balapan soared into the sky after the boat. The eagle shrieked as she approached the headland and at the sound Flint rushed out of the igloo. He saw Eska floating towards him and he threw up his hands and cheered, then he glanced across the beach to where Blu had been playing. He started forward, suddenly realising that his little sister was gone, then his face paled as he took in the eagle bulleting after the tail of a skin-boat gliding round the headland.

‘No!’ Flint screamed. ‘Not Blu! And Pebble!’

But the Tusk guard didn’t swing his boat round – he didn’t even hear the boy’s cry because it was lost in the shrieks of the kittiwakes and the wind. The boat disappeared out of sight and Flint tore across the beach, shouting his sister’s name again and again.

Eska didn’t wait for her iceberg to grind ashore. She leapt into the shallows, then raced over the snow after her friend.

Flint whirled round. ‘Why didn’t you warn me?’

He clambered on to the rocks that closed the beach into a bay and, ducking low, peered over the top. Eska grabbed him by the arm and they skidded down into the snow. Then she looked into his eyes and in the silence that followed she willed her friend to understand.

Flint gasped. ‘The Ice Queen has stolen your voice . . .’ And then he struggled against Eska’s hold. ‘We have to go after them! Blu’s in danger!’

Eska tightened her grip; she knew they wouldn’t win this way. They had to stay hidden. Because blowing the Frost Horn from the stars was the only way to put an end to the Ice Queen and rescue Blu.

Flint brushed his tears away as he listened to the faraway cry of the eagle. ‘Balapan . . . She’ll bring Blu and Pebble back, won’t she?’

Eska nodded.

Flint spoke quickly, his thoughts a tangle of panic and pain. ‘If Balapan fails, Blu will be made a prisoner, like Ma – so – so the Ice Queen won’t harm her immediately. Not until the midnight sun rises tomorrow. We still have time.’ The words were spoken as facts, but Flint’s voice was wavering. ‘If Balapan returns without Blu, she’ll be okay until we go for her – with weapons and – and a plan. Right?’ He glanced at Eska, then his shoulders slumped. ‘But if the Ice Queen already has your voice that means she can use it any time. We’re too late . . .’

Eska looked at her feet.

‘I should go after Blu now!’ Flint cried, kicking the rocks. ‘What better plan are we going to come up with?’

Again Eska held him fast.

‘I never should have left her outside on the beach!’ Tears sprang into Flint’s eyes again, but this time he didn’t wipe them away. ‘I should have been guarding her, and fighting for her, like Tomkin would have done. Not hiding in that igloo inventing!’

He spat the last word out with disgust, then sat down on a rock, his head in his hands. Eska did nothing for a few minutes. It was hard to work out what to do when there were no words left. Then she sat down, too, and, although she wasn’t sure whether warriors turned inventors really approved of hugs, she hugged Flint anyway.

They sat beneath the cliffs, but the eagle didn’t return and after a while Eska noticed the arm of Flint’s fur parka was stained with blood. She tugged at it and frowned.

‘Walrus blood, not my own.’ He sighed. ‘I used my Anything Knife to kill it after it knocked us off the iceberg.’ He turned the weapon over in his hand and Eska noticed the turquoise river gem in the hilt was gone. ‘We would’ve drowned if I hadn’t remembered, at the very last moment, what that stone contained.’ He paused. ‘I infused it with a wisp of the South Wind and, when I smashed it open and grabbed hold of a loose piece of ice with Blu, the wind blew us safely back to shore.’

Eska smiled, a smile that was full of pride and respect for her friend.

‘But I’m done with inventing now,’ Flint muttered. ‘It only ever brings trouble.’

There was a squawk from the sky and Balapan glided into the bay and landed, in a tumble of bloodied feathers, by their feet. Eska rushed forward and held the bird tight. Her wounds were not serious – once the eagle preened herself, most of the blood would vanish – but there was no sign of Blu or Pebble.

Flint hung his head. ‘My little sister . . . This is all my fault.’

Eska stood up and strode towards the igloo because Flint might be done with inventing, but she knew that his ideas were the only thing powerful enough to take her to the stars.

‘It – it won’t work,’ Flint stammered. ‘I was mad to think it would!’ He clambered back up on to the rocks and scoured the coast for his sister. But she was long gone. ‘We should be going after Blu!’

Eska carried on walking, with Balapan flying alongside her and the long white tusk raised in her hand. It shone like a slither of moonlight – it was impossible not to feel its magic – and at the sight of it Flint gaped.

‘You – you found the legendary Frost Horn!’ He hurried after Eska. ‘But just because you have it doesn’t mean my invention will work. It’s useless!’

Eska ignored him and broke into a run, then Flint was running, too, back towards the igloo. Eska disappeared inside, her heart thumping at what Flint might have made, but what she saw was not what she had been expecting.

Arrows fletched with snow-goose feathers to replace the quiverful she’d lost in the walrus attack. Eska tried to smile. She was grateful, of course, but how were these arrows going to take her and Flint to the stars?

‘I was just using the leftover snow-goose feathers to make you some more arrows.’ Flint looked at his feet. ‘The invention is behind the igloo. It’s too big to fit inside.’

Eska hurried outside where Balapan was waiting for her and there, tucked behind the snow house, looking more glorious than she could ever have imagined, was Flint’s latest invention.

A vehicle carved entirely out of driftwood, it balanced on three wheels – one at the front, two behind – and in the hollow scoop of the body there were two seats and a small lever in front. But most splendid of all were the wings mounted on wooden rods above the vehicle. Giant white wings made from the hundreds of snow-goose feathers Flint had gathered in the Lost Chambers.

Eska blinked. How could Flint have done all this since the walrus attack that morning?

As if he could sense her thoughts, Flint said, ‘I worked through the night to get it done.’

Eska’s baffled heart shone because here was a friend who, like Balapan, would never let her down. And as she looked upon Flint’s marvellous creation she felt a stream of memories flood back, of someone else whose loyalty and love blazed just as brightly as this. Her pa, Wolftooth, a large man with blue eyes and a gentle face, carrying her on his shoulders when she was very little, wrapping her in an eider-duck throw before a campfire, lifting her across the river’s fastest currents. Eska let the memories eddy around her, then Flint reached into his pocket and drew out a handful of little green gems.

‘Solidified glow-worm light,’ he said quietly. ‘Bottled at midnight during our stay in the Lost Chambers – Jay helped me when you and Blu were sleeping. Should shine bright when the night closes in.’ He glanced at the engine, a wooden cylinder stoppered by a stone. ‘Contains the loudest wolf growl ever heard in Deeproots and a bolt of lightning from the bottle we used on the Grey Man yesterday. But, even so, there’s no guarantee it’ll keep us going to the stars.’

Eska spun round and hugged Flint tighter than ever and Balapan ruffled her wings in delight.

Flint blushed. ‘I call it Woodbird. But I don’t know if it’ll fly . . .’

Eska grinned. Flint had lost his sister and his beloved fox pup. She had lost her voice. But here lay a way to reach the stars.