Every December since, on the longest night of the year, a winter festival has been held in the park.

It has become an annual tradition for Bianca and Finn to visit the rose garden at midnight and stand before the statue of Jack, Quilo, Pitter and Patter.

‘Do you think they’ll come this year?’ Finn asked, tucking his red scarf into the neck of his coat.

‘We’re here, aren’t we?’ Bianca replied, smiling up at her brother. He was taller than she was now.

They heard a familiar fizz, a crackle and a creak like the opening of an old door, and watched as the whites of Jack Frost’s eyes seemed to spread, infusing the granite sculpture with the properties of ice. Accompanied by a whip-crack snap, Jack stepped down from the pedestal. Quilo tumbled down after him, dressed as a bear as always, followed by the skittering Pitter and Patter.

‘You’ve got older and bigger!’ Quilo exclaimed.

‘You’re the same as ever,’ Bianca said warmly.

‘How is the Arctic?’ Finn asked.

‘The ice is still disappearing frighteningly fast,’ Jack said, looking mournful.

‘There are lots more of us now,’ Bianca reassured him. ‘Children all over the world are coming together, uniting to change things.’

‘Lots of people feel the same way we do.’ Finn nodded. ‘We don’t want the planet getting any warmer.’

‘And things are changing,’ Bianca said. ‘In the summer, the city council voted to stop burning all fossil fuels, and they’ve just finished building a big wind farm off the coast, in the sea.’

‘Oh yes! I like them!’ Quilo boomed. ‘It’s fun blowing those windmill sails around.’

‘We’re grateful you do,’ Bianca said. ‘It makes energy to heat and light our homes.’

‘Many of our vehicles are powered by the sun now,’ Finn said. ‘They don’t belch carbon into the sky any more.’

Quilo burped, and Pitter and Patter giggled.

‘The Ice Children are going out into the world and keeping their promise,’ Bianca told them proudly.

‘We all keep winter in our hearts,’ Finn said, putting a hand over his own.

‘Casper is on a ship measuring ice floes in the North Sea,’ Bianca told them. ‘He wrote to tell me that he’s finally seen a narwhal. And Sophie Lilley is in the mountains of France, still with skis on her feet, learning ways to keep the snow from melting.’

‘Gwen is the youngest-ever candidate for mayor,’ Finn said. ‘All her campaign promises are about preventing climate change. Her first act, if she gets elected, will be to change the name of the city to Winterton, to show the world how committed we are to preventing global warming.’

‘Catchy name,’ Quilo said.

‘Is that original? I’m not sure . . .’ asked Pitter.

‘I think I’ve heard it somewhere before,’ giggled Patter.

‘We’ve learned that it’s not enough for people to want change. Gwen says that it’s governments that make laws and tax businesses, and that we need to become the government,’ Bianca told them.

‘Yes, and we’re old enough to vote now.’ Finn nodded. ‘We can choose change and a way forward that will stop the Earth’s temperatures rising.’

‘We use our words and voices to protest the old industrial ways.’ Bianca’s hand went to the silver chain round her neck, and she caressed the crystal reindeer that hung there.

‘I go to university next year,’ Finn said proudly. ‘I’m going to become a climate scientist.’

‘What about you?’ Jack asked Bianca. ‘What are you doing?’

‘Well . . .’ Bianca found herself blushing. ‘I write. I’ve been making my own silver book, all about a city where children are being frozen in ice.’

‘I think I know that story,’ Quilo quipped. ‘Doesn’t it have a devilishly handsome boy in a bear suit in it?’

‘Yes, and he has a flatulence problem . . .’ Patter said.

‘. . . farts so powerful you can’t stop ’em.’ Pitter grinned.

‘I’m hoping it will end up on shelves in homes and libraries all over the world. And when children hear the story, or read it, maybe they will be inspired to think about the little changes they can make in their daily lives to become one of the Ice Children. That way we will always have a winter.’

Jack smiled. ‘I like that.’

‘Mum is buying Downy Falls,’ Finn told them.

‘She’s going to get a new printing press and fix up the factory,’ Bianca said, becoming excited. ‘She wants to make beautiful books that celebrate nature.’ She gave Jack a pointed look. ‘Without using mirror shards!’

Laughing, Jack clapped. ‘Wonderful. Now, who thinks we should invite my sister to our little gathering and decorate the city with snow?’

‘Ishild!’ Finn said breathlessly, looking up.

And, as if in reply, fat, fluffy flakes of snow fell from the sky, just like they always did on the longest night of winter.