Bianca’s scream ricocheted off the walls of Snow Haven. She ran towards the place where, only moments ago, Casper had been standing. Getting down on her hands and knees, she crawled to the edge of the hole that had swallowed him. It was a chute carved from ice, twisting and turning, disappearing into the glacier.

‘Casper?’ she called down it, but there was no reply, only the echo of her own voice.

Where had Casper gone? Was he in the dungeons? Was the monster down there?

Bianca moved away from the hole. She leaned back against the archway, hugging her knees to her chest. This was hopeless. They’d barely got through the door of Snow Haven and already Pordis and Casper had been captured. She’d never make it to Finn on her own. She dropped her head, feeling drained of energy.

‘You must go on.’ Pordis’s soft voice sounded in her head. ‘Find Finn.’

‘I can’t,’ Bianca said in her mind’s voice. ‘I’m so tired.’

‘They are frightened of you. Remember, they said that you could ruin their scheme, not just save Finn.’

Ruin their scheme? Bianca lifted her head. What did that mean? She’d been so determined to find and save her brother, it hadn’t occurred to her that she might have the power to stop Jack, Quilo, Pitter and Patter – whatever they were doing, or why ever they were doing it. None of the other children in Winterton had memories, only her, and she wasn’t supposed to have any. All their hearts were being frozen, including hers. Could she stop that? How? She had no idea. But, if she had the power to ruin Jack’s scheme, she was going to try.

Getting to her feet, Bianca steeled herself as she examined each of the archways leading off the lobby in turn. There were eight of them, and they appeared identical. She looked back along the passageway that had swallowed Casper.

‘If I were putting traps in passageways,’ Bianca muttered to herself, ‘I’d put one in the passageway that led somewhere important.’

Taking a few steps back, Bianca ran at the passageway and leaped over the hole that held the chute. Landing firmly on the other side, exhaling with relief, she crept forward carefully, testing the ground with each step. It was solid here. She continued towards an open door in the base of a tall tower. She poked her head through and looked up.

‘That is a lot of steps!’ she whispered to herself as her eyes followed the ever-spiralling staircase upwards. Something moved near her face. Jerking back in alarm, Bianca saw a translucent turquoise dragonfly flit past and rise up the stairwell.

Where did you come from? she wondered, turning around and studying the walls around her. There were no other doors or turnings. She stood in the middle of the corridor, reached out her arms so that they were touching both ice walls, then retraced her steps. Two metres back, the wall on her left stopped. There was an opening she had missed because everything was so dazzlingly white.

Holding her arms out in front of her, Bianca felt her way through the opening and came up against a wall. She turned, feeling her way around it, and drew in a surprised gasp as she found herself in a breathtakingly beautiful bower of ice flowers. In front of her stretched a path through a courtyard garden, the like of which she’d never imagined. Her eyes hungrily devoured every delicate detail. There were ice orchids growing at the feet of silver birch trees sculpted from snow. She gently touched a tiny cup-like flower that looked as if it were blown pink glass, and it tinkled. She spied frost fungus and snow mushrooms emerging from nooks in gnarled and knotted tree roots. Further along the path was an enclosed dell, carpeted with nodding snowdrops. In it a bone-white hummingbird was dipping its slender beak into the bell of a yellow flower blooming on a creeper with pearly leaves.

‘I knew you’d come here,’ said a cold voice. ‘That’s why we didn’t chase you.’

Bianca stumbled backwards in shock.

Standing below an icy lemon tree, bearing glassy fruit, was Jack. His strange, opal eyes seemed to bore into her. She took in the porcelain detail of the fine chin, thin nose and wild white hair, and knew this figure in front of her was as real as the flowers in this garden.

‘What have you done with Casper?’

‘Do not worry about him. He is with his winter creature.’

‘You trapped Pordis in a cage.’

‘Yes.’ Jack nodded. ‘It is you that I must deal with.’

‘Who are you?’ Bianca asked.

‘Who am I?’ Jack gave a mirthless chuckle. ‘I have many names. Sometimes I am a giant.’ The stick-thin body in front of her expanded, growing impossibly tall. ‘I have been a mother –’ a curving womanly figure now appeared as the giant shrank – ‘called Mrs Holle.’ A long beard of ice sprouted from the lady’s face. ‘I have been a grandfather, and many other things besides.’ The form and features of the creature in front of her returned to the ones Bianca recognized. ‘But you would call me Jack Frost.’

Awe and fear obliterated every thought in Bianca’s head.

‘How d’you like my garden?’ Jack asked, seeming genuinely interested in her answer.

‘It’s beautiful,’ Bianca replied truthfully, feeling every muscle in her body straining to run away. She knew now that she had been foolish. She couldn’t foil the plans of Jack Frost! And yet . . . Pitter and Patter had been worried she might. She stalled for time. ‘How do you get the colour in the ice?’

‘Ice is a crystal. It refracts light,’ Jack replied, and, seeing that this wasn’t enough explanation, went on. ‘Light is all colours. Make the crystal a certain shape and it will favour a part of the spectrum, giving a petal a blush of colour.’

‘I want my brother back,’ Bianca blurted out.

‘I wish you hadn’t taken that book,’ Jack said with a little shake of the head. ‘We can’t have brothers and sisters in Winterton.’

‘Please.’ Bianca could feel herself panicking. She hadn’t reckoned with facing something as ancient and powerful as Jack Frost. ‘Finn is my little brother. He needs me. I love him. Let him go.’

‘Love, meaning an intense affection or great liking of?’ Jack asked, giving a dictionary definition of the word.

‘Love is not just words,’ Bianca replied hotly. ‘It’s much more powerful than that. It’s a force that lives in your heart.’

‘Love is powerful?’ Jack looked interested in this idea.

‘Love is the most powerful thing in the world,’ Bianca replied defiantly.

‘In the human world?’

‘In any world.’

‘Interesting.’ Jack took a moment to consider this, then walked past Bianca, saying, ‘Follow me.’

As he moved away from the lemon tree, Bianca noticed that there was a door beyond it, in the wall of the fortress. What struck her was its utterly ordinary modern shape and appearance. It looked out of place in the exquisite garden of frost flowers.

‘You may see Finn and say your goodbyes,’ Jack said, walking away. ‘Then you will go back.’

‘Go back?’ Bianca spun round.

‘You cannot stay in Winterton. Your memory might spoil all my hard work. And, besides, it would be cruel to take two hearts from a family. You must think of your parents.’