As Eska approached two glistening columns of ice, she turned briefly to catch a last look at her friends. But what she saw made her insides roil.

A shattered iceberg. Water pulsing red. And one fur mitten floating on the surface.

Balapan screeched from her shoulder and surged into the sky, circling the crimson water again and again. Eska stood up – the horror drumming her bones, the anthem swirling in her ears – but, when Balapan landed at her feet with her head bowed, she threw back her head.

‘Nooooooo!’

The wail was a whisper – as she knew it would be – then suddenly the anthem cut to silence and, though Eska’s mouth was still open and her throat still thrummed, the word stopped. Just like that. Eska’s eyes widened and she scrabbled at her throat, then she swallowed hard and made to cry out again. But this time no sound left her body. Not even a whisper. And the reality of the situation dawned on her.

Flint and Blu were gone and the Ice Queen had stolen her voice.

Eska fell to her knees and wept. She had failed her friends. She had failed her parents. And now she had failed Erkenwald. Balapan wrapped her wings round her, but she couldn’t stop the tears. The Ice Queen had her voice and how long would it be before she used it to call the rest of the Fur and Feather Tribes under her command and tear down the Sky Gods? Eska sobbed silently for Flint and Blu. There was nothing left worth fighting for now.

The iceberg carrying the girl and the eagle drifted slowly on. Eska clutched at her throat and tried to find that hope she’d felt before, but it was gone, almost as if Flint and Blu had taken it into the depths of the sea with them, and, when she did finally look up, she saw that she was inside a tunnel carved from blue ice.

It curved over her head like a ceiling of turquoise jewels and it was only then that Eska realised how far she must have floated. She glided out of the tunnel and as she glanced down something caught her eye. Black and white shapes speeding beneath the water – sleek bullets with blunt heads.

Orcas, Eska thought.

A pod of these whales was nudging her and Balapan’s iceberg forward and though to Eska it seemed that her fight was over, it appeared the wild had a different opinion. And because of her unshakable bond with Erkenwald’s animals Eska looked ahead one more time, despite the grief that rocked inside her, to the last of the Groaning Splinters.

The final iceberg was a curve of white and it reared out of the sea like a slice of the moon. The orcas pushed Eska and Balapan on into a bay in front of it and then all but one of the whales vanished into the deep. The remaining orca surfaced and Eska held her breath at the sight of something so huge and fierce and wild. She looked into the whale’s eye and felt a memory hover close.

A woman with long red hair was rocking her back and forth while singing a lullaby about orcas and eagles. The memory slipped away and another surfaced. She was running now, hand in hand with her mother along the beach – and they were laughing. More memories of Blackfina flooded in: paddling a kayak beneath the stars, roasting fish inside an igloo, diving into the summer waves.

Eska gazed at the orca for several minutes, then she remembered the other name for this whale, the name her ma had taught her when she was a tiny girl.

Blackfin.

And suddenly it felt, to Eska, that while the Frost Horn might be miles away her mother’s spirit was close. The orca sank into the water and Balapan nestled into her side, but Eska could tell that the whale had not gone for good. Because a song began then, but not one composed of stolen voices like the Ice Queen’s anthem. This song was wild – it was the call of the whales – and the ocean around Eska hummed with it.

The whales sang with clicks and cries and long, drawn-out notes and Eska’s tears for Flint and Blu and all that she’d lost slipped from her cheeks into the water. And, as they fell, something rather extraordinary happened.

Another whale spiralled up from the depths, one with a speckled back, a white belly and a long, twisted tusk. A narwhal. The rarest of the whales and, if Eska’s memories of her ma’s words were true, it was known throughout Erkenwald as the unicorn of the sea. Its tusk broke the surface first, sparkling in the morning sun, and Eska blinked.

The narwhal dipped its head as if it had expected to see Eska all along, then it laid its tusk down on the iceberg in front of the girl. Balapan ruffled her feathers in anticipation and, hardly daring to breathe, Eska looked at the tusk. It was as long as her arm and wider at the end fixed to the whale’s head. She leant a fraction closer and saw a symbol carved into the ivory around the tip.

It can’t be . . . Eska thought.

But it was. A carving of the Sky God’s constellation, just like the birthmark on her neck.

But why would a narwhal bear the mark of the Sky Song? Eska wondered.

Balapan took a small step forward and dipped her head and Eska, not wanting to seem impolite, dipped hers, too. Then the narwhal shook its body and pulled back from the iceberg, sinking into the sea. Its tusk, however, remained on the ice and Eska realised then that the North Star had given something very precious to the rarest whale in the kingdom.

The tusk was the long-forgotten Frost Horn.

Eska’s eyes grew large as she picked it up. She had found the Frost Horn, but it had come too late for her poor friends, Flint and Blu. The lump in her throat grew. Perhaps now that she had the horn though there was still time to stop the Ice Queen from using her voice? And, as the orcas pushed Eska and Balapan’s iceberg back through the Groaning Splinters, Eska knew that her fight wasn’t over yet because here, in her hands, was hope.