‘I don’t understand!’ Bianca grabbed at Jack’s coat. ‘Why are you freezing children’s hearts?’

She cried out as the hand that clutched the cloth of Jack’s coat tails became translucent as ice. Letting go, she stared in shock at her fingers as they became pink and fleshy once again.

‘I am not freezing your hearts,’ Jack replied calmly. ‘You read The Vanishing World. You opened your heart to winter. You called for the Snow Queen to come. You invited her in.’

‘I . . .’ A memory of the spellbinding words inside the silver book appeared in Bianca’s mind, and she knew she had uttered them: I wish the Snow Queen would come. The world is too hot . . . Please come, Snow Queen. My heart longs for you. It’s yours. Take it. Make it snow. Make it snow. Make it snow.

‘That book was a trap,’ Bianca protested. ‘None of us knew what was going to happen to us.’

‘Shall we go and find Finn?’ Jack turned away.

‘Answer me!’ Bianca shouted. ‘What do you want with our hearts?’

‘Are you blind, Bianca?’ Jack’s voice became a melancholy whisper. ‘Do you not see what is happening around you?’ Leaning down, Jack forced her to look into his unreadable eyes. ‘Winter is dying, Bianca. Our time gets shorter every year. You humans have made the world a place in which we cannot survive.’

‘No, I . . .’ Bianca gasped in breathless protest.

‘The first to go will be the queen, bringer of snow, but I will soon follow. Then it will be farewell to Pitter’s hail and Patter’s sleet. Quilo will become summer’s minion, no longer blowing cold, but hot.’ A tilt of the head. ‘I know you understand. We’re the same, you and I. You’re here to save your brother, Finn. I am saving my sister, Ishild.’

Jack’s words blasted into Bianca’s core, and her mind reeled at the revelation that she’d been spying on and fleeing from Frost, Hail, Sleet and the North Wind.

‘That is the story The Vanishing World tells,’ Jack explained. ‘You and every other child in Winterton read it and recognized the truth. That is why you offered up your heart to the Snow Queen. You gave your heart to make it snow.’ A sigh suggested this was a rare and wonderful thing. ‘Finn was the first to give his heart, so that Ishild might live. He is special. From his imagination I plucked Winterton. That is why he can never leave.’

‘Please don’t take Finn’s heart,’ Bianca begged. ‘Please.’

‘We take nothing,’ Jack replied. ‘He gives it freely.’ He drew himself up. ‘If anything, I have been benevolent. Especially considering what humanity has done to me. In exchange for their hearts, the ice children will live here, in wonderful Winterton, playing happily forever, and they will never be sad because they will never remember their past lives. It’s every child’s dream.’

‘Wait!’ Bianca reached out to grab Jack, but stopped herself just in time. ‘There isn’t only a story in that silver book. I saw you put something in there. “Mirror splinters”, Pitter said.’ She leaned forward as close as she dared. ‘What was it? Why did you do that?’

‘That? Oh . . . that was nothing.’ It was the first time Bianca had seen Jack ruffled.

‘Then you can tell me what it was.’

‘It was merely a mirror splinter.’ Jack pivoted and stalked away from her, out of the frost garden.

Bianca’s mind whirled as she hurried after him. A mirror splinter? Why is there a mirror splinter in each book?

‘Shall we take Finn’s favourite route to the throne room?’ Jack said in a perkier tone once they’d got to the passageway. ‘I made this for him when he first arrived at Snow Haven.’ Pointing a finger at the opening of a slide that Bianca could have sworn hadn’t been there when she’d passed this way earlier, Jack said, ‘Climb inside. Let’s ride the Snow Haven Slide.’ Grabbing the top of the slide, Jack jumped in, disappearing with a whoosh.

Bianca stared down the slide, paralysed by indecision. She didn’t want to climb inside. Where might she end up? In the dungeons, perhaps. She only had Jack’s word that Casper was with Monodon. And then Monodon’s warning came back to her: ‘There’s something terrible in Snow Haven. Something dying.’ And she was stunned, understanding all of a sudden that it was winter itself, the season of death, that was dying. Her adversaries – Frost, Snow, Hail, Sleet and the North Wind – were winter’s elements. They were more ancient and powerful than gods, yet they were fighting for their very existence.

The Earth needs winter, she thought. I don’t want it to disappear. I love winter.

Bianca climbed into the mouth of the slide. ‘Once I’ve rescued Finn, I will find a way to save winter,’ she whispered fiercely. ‘If they must take a heart, then let it be mine.’

Drawing in a deep breath to steady her nerves, she gripped the side of the slide and pushed herself off.

The ice curving around her glowed blue. At first, the descent was gentle, but she soon picked up speed as the slide dropped steeply, before being whisked upwards, carried by the momentum of her fall, speeding so fast she was barely touching the surface at all. A sharp turn sent her slithering up the wall, then corkscrewing down, round and round until she was deliriously dizzy. She gasped as the roof of the slide disappeared, showcasing a cloudless blue sky. Fighting gravity, she raised her head a little, and saw she was whirling around the outside of one of the giant towers. Plunging down suddenly, wailing at the thrill of rocketing out of control round another bend, Bianca finally gave in to the joy of sliding, letting herself go as she plunged into darkness, speeding round bends and down until she shot out into a huge mound of soft, fluffy snow.