Grace had never seen Ma look like this, as if she had been rubbed out and then drawn all over again without any colour and with twice as many lines and wrinkles. In contrast, Dad looked almost indecently healthy and cheerful as he raced around phoning people, and then the police, and then flying in and out of the house to check everywhere he could think of. But Grace knew that the frantic running was just his own way of dealing with the terror.

The first time he left, while Grace cuddled a sobbing Maggie on the sofa, Ma turned to her with enormous dark eyes. Grace saw the accusation in her expression, and she flinched. She almost wished that Dad was still there. He didn't seem to read Ma's thoughts in the way Grace did, but then he hadn't known her as long. Ma and Grace had been a duo for six years.

Faced with Ma's expression, she found words tumbling out before she'd even had a chance to plan what she would say.

"When Benjamin tried to get up on the stage, in the light show, I stepped in instead. The guy doing it asked him if he wanted to be tested, and I thought... that there was something wrong. He had this glass globe, and I took it, and it shone so brightly it hurt my eyes."

Ma's face was absolutely still, but Grace waited for her before saying anything more. In the end, her mother croaked, "Did he give you anything?"

"A gold coin, but I didn't want it." She remembered Benjamin snatching it out of the air with triumph, and closed her eyes for a moment. "Benjamin took it."

She opened her eyes to look at Ma, expecting her to shout at her, but her mother was looking away from her, her eyes still big and round and terrified as she looked at something that Grace couldn't see.

"What did he look like, the man on the stage?"

"Strange," Grace told her. "His eyes seemed to change colour, like the lights in his show. I thought it was a trick but I couldn't see how he was doing it. He had blond hair tied back, and he was tall. Taller than Dad, but... bigger."

Ma nodded, lowering her head, and the way she did it made Grace stare. It was as if Grace had just confirmed something she already knew. But how could she have known?

"Ma, what is it? Who was he? Do you know him?"

But the doorbell chimed, the police arriving, and Ma got up quickly, never once looking at Grace as she let Lieutenant Doorig and his pretty Deputy in and began trying to explain what had happened.

Grace had trouble focusing on the two officers, even when they started asking her questions. She was looking at her mother, and wondering how much she had been hiding. She kept having to ask them to repeat themselves.

"So you don't think he had any reason to run away?" the Lieutenant asked her, for the third time, and she finally looked at him in confusion.

"He's eight years old, and afraid of the dark. Why would he run away in the middle of a freezing night? It makes no sense at all."

The Lieutenant nodded, though she could tell he wanted to disagree.

Grace didn't want to hear more about Benjamin running away. She wanted to know about the other missing children, and she asked, before he could say anything else, "What about the fair?"

"The fair?"

"Yes. I told you we went to the fair, so have you been to talk to them?"

"We've got officers on it," Doorig said, and looked like he was about to ask Ma something. Grace didn't let him do more than open his mouth.

"Was the fair at Saranac Lake yesterday? Did that little girl, Kelly, go?"

The Lieutenant stopped, with his mouth slightly open, and glanced over at his Deputy. Grace didn't need to know anything else, but she didn't miss the way Ma stared at her. She knew that Grace had kept the disappearance from her, and that this was her fault. All of it.

She sat back in her chair and brooded, helplessly, while the Deputy asked Ma what Benjamin might have been wearing, and whether he had any noticeable features.

She was midway through a detailed description of Benjamin when Dad's key scrabbled at the lock, and then the door opened clumsily. He erupted through it, his cheeks red from the cold and his hat on wonkily. He didn't even seem to notice the two officers. He only looked at Grace, and she felt like he was trying to communicate something to her.

"I went back to the fair to ask if he'd gone back there, but it's gone too."

Grace heard her mother say quietly into the silence which followed, "Of course it has."

Grace's mother offered no word of explanation until after midnight, when Maggie finally fell asleep curled on top of Dad, who dozed off shortly afterwards. The day had become a nightmare of frantic activity contrasted with long periods of waiting, and the police had left the Deputy with them until nightfall to keep in touch with the other officers. In the end, she had gone off-duty with a supportive smile and a few empty words of hope and encouragement.

Grace's stomach felt empty and tangled, and she couldn't remember whether or not she'd eaten any of the sandwiches Dad had gone and bought in one of his many trips out. He'd alerted most of the neighbourhood, and they had all been out searching too, he said, checking the snow for footprints and opening every room and building they could. And of course he'd asked whether anyone had seen or heard anything in the night, but the house was in High Peaks' suburban south, populated by young families and old folks. None of them had been awake past eleven, though they all felt guilty about it now.

Grace and Ma sat staring at the fire Dad had lit for a while, with questions welling up in Grace which she was half frightened of asking. But in the end, her curiosity bubbled up too high for even her fear to keep down, and she whispered, "Who was that man, Ma? You know him, don't you?"

Ma looked over at her, startled, as if she had forgotten that Grace was there, and then she sighed and looked down at her hands, where she was turning one of her rings round and round on her finger.

"I used to know him. I haven't seen him since I came here."

"He's Russian?"

Grace saw the way her mother half-smiled, and she felt as if the ground had been pulled out from under her.

"Ma?"

There was silence from her mother, and Grace's frightening sense of something wrong grew.

"Ma, where did he come from?"

She watched the way Ma breathed out a long, tired breath. She seemed to collapse just a little.

"It's hard to explain when it's somewhere you won't have heard of. We just called it The Kingdom, or The Walled Kingdom, but it's part of an entire world which we never bothered to name. If I think about it now, I think of it as the Cold Lands, but that's just my name for it."

Grace's heart stepped up, until it was pounding in her chest, but not with disbelief. With Ma's words, so many things fell into place that she wondered how she could have missed them before: Ma's reluctance to talk about where she had come from, her difficulty fitting in to this world, and her strange and exotic clothing which had gradually given way to a more American sort of dress.

"We?" she whispered. "You're from there, too. Aren't you, Ma?"

Ma nodded, slowly, and Grace didn't know whether to be distraught or exultant. She wasn't just a misfit, she realised at last. She came from somewhere different, maybe somewhere which would make sense of everything she felt.

 "Is it... a long way away?"

"Sometimes." Ma looked back at her hands. "It's close to us at certain times: in winter, and at night. Closest still in the moonlight. We share a moon with that world, and the fabric between us is so thin that it sometimes vanishes and lets people cross. Most of them cross by accident, during a winter full moon, but some come with a purpose."

Grace watched her mother as she turned the ring again and again on her finger. "Why did you come?"

"I fled to save you," Ma said quietly. "You have to understand – everything is different there. Here, things are ruled by what is not possible. That's how physics works, you know; by its limitations. There are rules and laws for everything, from gravity to heat exchange. It took me a long time to get used to them."

"But not there?"

"Not there. What is possible is... stronger. Possibility itself is a force that certain people can manipulate."

Grace leaned forward in her chair. "What do you mean?"

"They're like wizards. They can do things which other people can't, but it's not magic, it's just a world with fewer rules. Some people are born with particular – well, they're like muscles. They're part of the body. They give them power over what is possible. And those people who have them – the riezehn - can work possibility to do things you would call magic."

"Like the light-show," Grace said, the sick feeling growing and twisting around something which was a little bit like excitement.

"Like the light-show," her mother agreed. "And you made the globe shine because you're one of them, as I knew you would be."

The truth seemed to be the only relief Ma could feel now. There was no resistance to Grace's questions, and she knew that she needed to find out what she could while Ma was willing to tell her.

"So why did you run?"

Maggie, on Dad's lap, stirred and murmured slightly, and Grace reached over to stroke her hair gently until she fell asleep again, watching the pale face with its blotchy skin under the eyes and feeling a desperate need to comfort Benjamin in the same way. Was he alone? Was he cold? Was he frightened?

"Because the riezehn aren't free," Ma whispered. "Boy-children are snatched the moment they show any talent, and taken to the tower where the Queen rules, as she's done for centuries."

"Why?" Grace asked.

"She uses their power," she said, her eyes focused on nothing. "The boys are kept in a form of trance, and magically linked to make them more powerful."

"What does she need their power for? Isn't she magical herself?"

"She is, and she's strong," Ma told her. "But she isn't the strongest. And yet she wants to rule. And not just to rule, but to rule in absolute luxury and wonder. Her palace is the most amazing creation. It's beautiful, but it shouldn't exist, never mind withstand centuries of change. She uses the power of the boys, the poor little things,  to keep her fantastical palace working."

"Their whole lives?" Grace whispered, feeling suddenly cold.

Ma shook her head. "Until she has drained them; until they are no longer any threat, and no longer any use to her. Then she sends them back to their families. But they aren't the same any more."

There was a catch in her voice, and when Grace looked over, she saw that Ma was crying; big, shining tears rolling down her face.

"I can't bear it, Grace. I can't bear for him to be kept like that, enslaved, barely aware of what's going on around him until he's all but mad from it."

"Is that why they took him?" Grace asked, horrified. "Because he had the coin which meant he was magical?"

Ma rubbed at her eyes. "I'm not sure. I think that's what they will do, because Ruidic wouldn't have asked for him to be tested if he hadn't had some talent. Ruidic can see ability, though not how strong it is, which is all that saved me."

"What saved you?" Grace leaned forwards again. "I thought it was just the boys they snatched?"

"I said it was the boys they kept in captivity," Ma told her. "Girls can't be linked, so anyone weak in possibility would be ignored. They didn't pose any kind of threat. But the strong ones, the ones born with a real raging power – they vanished."

Grace nodded, slowly. "You were one of them. You were powerful."

"Yes," Ma said, tiredly. "And I hid it in order to survive. I pretended to struggle to tip a cup over or blow out a candle, when I could have lifted the whole of that wretched tower up and blown it apart if I'd wanted to. If they hadn't stopped me, of course. They're good at stopping people from doing anything to threaten them." Her mouth twisted in a smile that made her look ugly, and not like herself. "It wasn't hard to find out how to use their magics to travel between worlds. They'd sent Ruidic and his fair so many times to find children with talent and snatch them away."

There was a silence, while Grace thought about this strange world. For some reason it was not difficult to accept it, perhaps because Benjamin had gone and because she had sensed something herself last night at the fair. The hardest thing to accept was that Ma was really powerful, instead of creative, and disorganised, and a little bit neurotic – a word Grace had heard her father use about Ma a few years before, and which had got him into a lot of trouble.

But there a question burning in her, one she felt unable to ask even though she thought she knew the answer. It was one she had asked time and time again as a child until her mother's anger had stopped her, and now it was buried so deep within her that she couldn't voice it. Instead, it whispered within her: Who was my father, then?

It mattered almost as much as anything had mattered to her in her life. But not as much as Benjamin did.

She turned back to Ma. "You have to go after him."

"I can't," Ma said, and there was heartbreak in her voice. "I can't, because that's what Ruidic wants me to do, and he'll be waiting. He'll never let me out."

"But you're powerful-"

"And so is he." Ma turned to her, a fierceness in her face and in the still-whispered words. "I won't even reach Benjamin before he stops me. I'll die, and that will mean there's no-one to protect you and Maggie, Grace. For as long as that world brushes up against ours, you will be in danger."

Grace felt cold. She thought about Benjamin again, and how he'd tried to hide his fear when he climbed up onto the stage, and she wanted to slap her mother.

"You can't leave him there," she said.

"What can I do?" Ma asked, in a harsh whisper. "What can I do when going after him will put you and Maggie in danger? I need to take you both away, somewhere he won't think to look, at least not for a long time. Then, maybe, if you can be safe, I'll go there. In a few months."

"A few months?" Grace was aghast, imagining her brother frightened alone for week after week. "But it's Benjamin-"

"Do you think I don't care?" Ma was crying again, and she looked at Grace with so much pain and guilt that it made her feel sick again. "Do you think I can stand to think of my little boy, who isn't nearly as brave as he pretends, on his own with them? Scared, and in danger, in a world he doesn't understand? But I have to look after you."

"You can't," Grace said, forgetting to whisper, and Dad jerked upright.

"What time is it?" he asked, thickly.

"Nearly one," Ma said, rubbing at her eyes again.

"I should get Maggie to bed," he said, and shifted her on his lap so that he could stand. Once on his feet, he swayed slightly, and then walked over to the door and disappeared out into the hallway.

Grace listened to him climbing the stairs heavily, and looked back at Ma. "But Maggie might be all right. If she isn't riezehn, then they wouldn't want to take her, would they?"

"She is, Grace." Ma let out a breath. "I can see it burning in her in the moonlight, just as I can see it burning in you and Benjamin. It's like a living fire, and it's in all of you. I can see it, just like he can."

Grace sat still, even though her body was screaming at her to move, to get up and go after her brother.

"But there is a way to get there, isn't there? I could find a way."

"No!"

Ma sat up so quickly that Grace flinched.

"Why not?"

"You don't know anything about that world. You'd be picked up within days, and unlike me, you wouldn't know how to pretend. You held that orb of Ruidic's, didn't you? You made it shine blindingly without knowing how, because you can't control an ability that only comes to you in bright moonlight." She reached out to take Grace's hand, her fingers cold and hard like metal and so very unlike Ma's usual soft touch that Grace flinched. "And he knows now, Gracie. He knows what you are."

Grace stared back at her, her own eyes starting to fill with tears.

"Teach me how to control it, Ma," she said.

"It takes years, Grace."

"Please-"

The sound of Dad's footsteps on the stairs again silenced Ma. She looked anxiously at her daughter, and then let go of Grace and looked down both of her hands again, where she began to twist the ring round and round again.

When Dad returned, he glanced at Grace, and at Ma, and then came and sat with Grace on the sofa.

"You ok, Gracie?"

"I want to go and look for him," Grace said, her mouth twisting as she tried not to cry. "Tell Ma to let me go and search. I could find him-"

"You can't go in the dark," Dad said, immediately and firmly. "But – I'm going back out again anyway. I'll look, I promise, Grace. I'm not going to stop looking."

Grace let him hug her, and then he stood and started to collect his hat and gloves, despite his weariness. He had been out searching for almost fifteen hours, and he was still going again.

"Let me come," Grace said, getting up and picking her own coat up. "I'll come with you and help. Keep you company."

Dad hesitated, but he was tired enough to give in. "All right. Come with me. But we'd better bring cookies and coffee or you'll be dead on your feet within an hour."

Grace hurried through to the kitchen and filled the kettle while he dug cookies out of the cupboard, and then a flask. She felt dizzy with the thought that they wouldn't find anything, but she couldn't bear to stay here with her mother, who was going to do nothing. Even if Grace understood why, she couldn't accept it.

She knew that it was up to her now, and that she would have to find a way of travelling to that other world. If Ma knew how, then Grace would find a way too. She had to.