Pordis trotted happily through the snow-covered forest. Staying on the reindeer’s back wasn’t as hard as Bianca had feared. As she relaxed, she looked around.

A reverent awe fell upon her as they travelled through the ancient trees, their branches bowed with the weight of trillions of ice crystals. Their cracked bark, the broad girth of their trunks and their soaring height led her to believe the trees were hundreds of years old, maybe thousands. From the reindeer’s back she saw human and animal footprints in the snow and wondered whether one of those sets of prints belonged to her little brother.

When they emerged from the fringe of the forest, Bianca blinked as her eyes adjusted to the dazzling landscape. They were at the top of a snowy slope that stretched down to the shore of a deep blue ocean. There were icebergs off the coast. Chunks of sea ice as big as trampolines floated about in the cove below. A pair of penguins dived from one, chasing a fish supper. Bianca closed her eyes, drawing in the fresh sea air, tasting salt on the back of her tongue. ‘Oh, Pordis!’ she exclaimed, blinking them open. ‘This place is heavenly!’

‘Yes,’ Pordis agreed. ‘I belong here.’

Bianca found she was smiling. Her soul felt as light as the black-capped Arctic tern she spotted scything through the sky with fanned-out tail streamers. The snowy slope was as untouched as a blank page. Bianca resisted the delightful urge to slide off Pordis’s back and roll down it. ‘Look! There!’ Further along the shore, Bianca could see a chain of twinkling lights decorating a path that started in a cove and disappeared up through snow-capped rocks. ‘I think we need to go that way.’ She felt a spark of excitement. ‘How do we get there.’

‘I’ll find a way. Hold on tight!’ And suddenly Pordis was running, her long pink tongue hanging out of her mouth, black nose held high, head moving left then right, as they flew down the hill together.

Bianca clutched Pordis’s antlers tightly, sucking in her breath as they raced towards the cliff edge. Pordis turned, galloping along the clifftop, putting on a burst of speed, her hooves kicking up snow. Bianca’s hair flew back from her face, and she released her breath with an exhilarating ‘WHOOP!’

Reindeer and girl cantered along the coast together, slowing as the land dropped down towards the sea and became rocky. Their path was full of twists and turns, and Bianca marvelled at Pordis’s sure-footed skill.

‘You’re like a big, beautiful goat with antlers,’ she declared happily.

Pordis stopped abruptly. ‘And you are like a big, bald monkey!’ she retorted tartly.

‘Oh! I’m sorry.’ Bianca suppressed a giggle at the reindeer’s indignant head shake. ‘I didn’t mean to offend you, Pordis.’

‘I am a magnificent caribou, a regal reindeer. I did my best and fastest running, and for what? To be likened to a goat! Is a goat magnificent?’

Bianca tried to contain her giggle, but it exploded out of her nose with a snort, which was quickly followed by laughter. The next thing she knew, she was landing sideways in a snowdrift, having been shrugged from Pordis’s back.

‘Oh, Pordis, I am sorry,’ Bianca said, getting up and dusting herself off as the reindeer trotted away towards the cove with her nose in the air. ‘I am a silly old bald monkey and you are magnificent. Please forgive me.’

Pordis stopped walking. ‘Bianca, there is a boy by the sea.’

Bianca ran to the reindeer’s side. She saw a boy in maroon pyjamas, sitting cross-legged on a rock at the tide’s edge, looking out to sea. ‘Casper!’ she said, finding she knew his name.

The boy turned his head and, seeing her, looked puzzled.

‘It’s me, Bianca,’ she said, scrambling over the rocks towards him.

‘Bianca . . .’ Casper repeated, getting to his feet to greet her politely. There was no flicker of recognition in his eyes.

‘Hi.’ She blushed, suddenly feeling shy. The orange book in her pocket said she had been to this boy’s house, but all her brain could offer her was a will-o’-the-wisp memory of Casper’s kind brown eyes and generous smile.

‘What are you doing here all alone?’

‘Oh, I’m not alone,’ Casper replied. ‘And people keep arriving. Like you did just now.’

Bianca wished she could remember where she knew this boy from. His cheerful voice and open manner were so familiar. ‘How long have you been here?’

‘I’m not sure. Not long,’ he replied with a shrug. ‘But maybe . . . always. What about you?’

‘Yes. Same. Not long. I think.’ Uneasiness fluttered in Bianca’s chest like a shadow moth. Why couldn’t she remember? ‘I’m trying to find my brother, Finn. He’s five and looks a bit like me, except with blond hair and blue eyes. Have you seen him?’

‘No,’ Casper replied, turning away as something out to sea drew his eye. ‘Two other girls have come through here, and a boy with dark hair.’

‘Why are you wearing pyjamas?’ Bianca asked.

‘Why aren’t you?’ Casper countered with a grin. ‘The others were. I think it’s what we wear here.’

‘Do you remember where you were before you came here?’

‘No.’ Casper shrugged, looking back out to sea. ‘But I think this place is all that matters.’

‘Well, if you see my brother, can you tell him I’ve gone that way?’ She pointed to the path.

‘Mmm-hm.’ Casper nodded, his eyes still fixed on the waves.

‘What are you looking at?’ Bianca asked, stepping onto the rock beside him.

‘Monodon.’ Casper pointed, and Bianca saw that there was a pod of whales swimming in the bay. One of them had a long tusk protruding from its head. ‘He was waiting for me when I arrived. He took me on his back. We swam right out of the cove.’

‘You rode a narwhal?’ Bianca was amazed.

‘If you go out far enough, you can see round that fortress on the glacier.’

In the distance, Bianca saw a glacial promontory with a towering castle of ice perched on it like an albino vulture, its translucent claws gripping the cliff edge.

‘I think we’re on an ice shelf,’ Casper said.

‘Floating out to sea?’ asked Bianca.

‘Yes.’ A glazed look came over Casper’s face.

‘Is Monodon talking to you?’ Bianca asked, suddenly realizing why he was behaving strangely.

Casper’s eyes flickered back to hers and he nodded.

‘Pordis talks to me too.’ Bianca looked over her shoulder and smiled at the reindeer. ‘She’s cross with me, though, because I said she was like a big goat. I meant that she was agile . . .’

Pordis huffed and lifted her nose in the air. ‘Bald monkey!’

Casper laughed. ‘Monodon says I can go and play with the other children, but I’d rather stay here with the whales. They’re much more fun than fairground rides.’

‘Fairground rides?’

Casper nodded to the path. ‘Up there. That’s the way all the others went.’

‘I think we have to go that way too.’ She looked at the sulking reindeer. ‘Come on, Pordis.’

‘I hope you find your brother,’ Casper said. ‘If I see him, I’ll say you’re searching for him.’

‘Thank you. His name is Finn.’

Pordis walked by Bianca’s side up the track through the rocks. Overhead, vines of twinkling lights were strung in zigzags. At the path’s end, suspended between two skinny fir trees, was a glittering sign in giant swirling letters of ice that said WINTERTON.

‘What is this place?’ Bianca whispered in wonder. Rising before her was a huge Ferris wheel shaped like a giant snowflake. A blue neon sign proclaimed it to be the Flurry Flake. She saw a helter-skelter carved from ice and a waltzer with pretty glass carriages. Beyond the funfair, mountains emerged from the snowy plain on which Winterton was built.

Tinkling music played softly as she and Pordis strolled through the fairground. ‘All the rides are empty.’ Bianca peered about. ‘Where is everybody?’ A heavenly smell turned her head. In the centre of a square of food stalls was a fountain bubbling with steaming hot chocolate. Hanging around the rim of the fountain was a rainbow of colourful tin mugs.

‘Oh! I’m starving. Come on, Pordis. Let’s have a mug of hot chocolate.’ She skipped over, excited to try the fountain. At its four corners were enormous white planters containing what she thought were decorative trees. She inspected the strange squishy pink fruit that were hanging from their delicate clear branches. ‘Marshmallows!’ she declared with delight.

Plucking one, she nibbled it cautiously, before putting the whole thing into her mouth and savouring the sweet taste. ‘Delicious!’ She picked three more, dropping them into a purple tin mug, which she held out under the stream of frothing hot chocolate. ‘I can’t have been here before,’ Bianca said to Pordis, sighing contentedly as she drank deeply. ‘I’d definitely remember this.’ She perched on the edge of the fountain and refilled her cup.

On the far side of the square was a frozen-fruit stand with a sign saying HELP YOURSELF. Gulping down her drink, Bianca went over and picked up an empty punnet, filling it with frozen strawberries and raspberries. She beamed at Pordis. ‘I wonder what else is here.’ She popped a handful of tangy berries into her mouth. ‘Let’s explore.’

Arranged beneath giant toadstools, the size of caravans, were cosy rugs scattered with cushions. Red paper lanterns sat on mushroom tables, making the snow around them glow pink.

‘Oh, look, Pordis! Up there. Someone is on that slope. They’re skiing!’

A figure in a green nightshirt and shorts zoomed down the hill, long honey-coloured hair flying behind her. When she reached the bottom, the girl leaned to one side, turning, carving the snow in a semicircle with the blades of her skis, till she came to a neat stop.

‘I know her, Pordis!’ Bianca exclaimed, running towards the girl and waving. ‘That’s Sophie!’ Pordis trotted by her side, but they both stopped suddenly when they saw a large cat bounding down the slope, its huge paws barely leaving a print on the snow. It had silver fur, leopard-like spots and a long, bushy tail. For one terrible moment, Bianca thought the cat was going to pounce on Sophie and eat her, but instead it rubbed its head affectionately against her side and Sophie scratched behind its ears.

‘Sophie, it’s me, Bianca!’ she called out as they got closer.

‘Hi,’ Sophie called back, looking at her with no sign of recognition. ‘Do you want to come up the slopes and ski with us? The powder is as fresh and fluffy as eiderdown stuffing.’

‘Er . . .’ Bianca stared at the cat, who glowered back with unblinking eyes. ‘No thanks.’

‘Oh, don’t mind Lumi,’ Sophie added. ‘She’s a friendly snow leopard. Aren’t you, Lumi?’ She tickled the big cat’s chin. ‘Come on. It’s brilliant up there. When you’re at the top, you can see right across Winterton.’

‘Oh, all right,’ Bianca said, walking forward, but then she stopped and frowned. ‘Hang on. No. I can’t. There’s something I’ve got to do first. Er, what was it?’ She scratched her head and spotted the little red scarf around her wrist. ‘Oh! I’ve got to find my brother!’

‘Have you lost him?’

‘I . . . I must have.’ Bianca felt a jolt of alarm that she had forgotten Finn in the short time it had taken her to get from Casper to Sophie.

‘Well, I can see all the children arriving from up there.’ Sophie pointed up the slope. ‘I saw you and your reindeer come out of the forest.’

‘Is everyone here a child?’ Bianca asked, feeling uneasy. She couldn’t put her finger on it, but there was something about the wonderful Winterton that didn’t feel right.

‘Yes. Isn’t it great?’ Sophie unclipped her skis. ‘Right, we’re going back up.’ She climbed onto Lumi’s back. ‘What’s your brother’s name?’

‘Finn. He’s five. If you see him, tell him I’m in the fairground, looking for him.’

‘Got it,’ Sophie said as the snow leopard padded away. ‘See you later!’

Bianca watched the big cat bound up the mountain.

‘You wouldn’t dare call Lumi a big goat,’ said Pordis.