David stood in the hall and buzzed Petra’s door, bracing himself for the worst. After a moment it slid open.

“Hi,” he said. “Um … can we talk?”

Petra let him in without saying a word. David wasn’t sure how best to handle this frosty reception, so he just came straight out with it.

“Petra, where was Eddie’s study? I mean, Sir Edmund Utherwise’s study? You know, the one in the photo the professor showed me when I first got here. Was it in Unsleep House somewhere?”

“Yes,” said Petra. “His study is on the top floor of the château. Sir Edmund hated it down here. He called it ‘the mole hill’ and refused to be moved. Why?”

“Is? You mean it’s still there?”

“Yes. They just locked it up when he died. The science guys want to keep it exactly as it was. A sort of museum for them, I guess. What is this, David?”

“Listen, I need to get into the château. I want to look in the study. How can I do that?”

“You can’t,” said Petra. “You’re under house arrest, remember? You can’t even leave the Lodge without an escort.”

“But what if I weren’t under arrest?” said David. “How do you normally get to it from here?”

“There’s a tunnel from the upper level of the base that leads into the cellar of the château,” Petra said. “But you would never get there. The upper level is heavily guarded these days.”

“Isn’t there some other way? There must be a fire escape or … or whatever. It’s very important. I think I’ve found something.”

“Oh?” said Petra, her face stonier than David had ever seen it. “Like what?”

“Look, Petra, I’m sorry about what happened at the station, about making a fool of myself, about … everything. I just want a chance to put things right. Help me get into the château and I’ll show you.”

Petra stared at him for a long time before she spoke.

“They assigned me to protect you, David. That’s all I’ve ever done. If I’m going to help you now, I need to know that you will trust me from now on, without hesitation. So will you?”

“I will,” David replied. “I couldn’t wish for a better bodyguard than you, Petra. And I really am sorry.”

Petra thought about this for a moment. Then she gave David a brilliant smile.

“Good,” she said. “Because I already have a plan.”

“I hope you don’t mind other people’s underwear.” Petra grinned.

David tried to keep calm as she wrapped a sheet tightly around him. He couldn’t take his eyes off the laundry chute hatch in the corner of her room. What kind of plan was this?

“Are you sure this is the only way?”

“Yes, stop fidgeting.” Petra seemed to be enjoying herself. “There’s always a pile of dirty clothes at the bottom. Well, almost always. You’ll be fine.”

When Petra had finished he had to hop to reach the hatch.

“This is ridiculous,” he protested, trying to hide his alarm. His arms were bound tightly at his sides, and he suddenly realized he was going to have to go headfirst.

“You want to get out of the Lodge, don’t you?” said Petra, not quite suppressing a laugh. “I’ll meet you in the laundry room in five minutes.”

“But is it steep?” David peered into the dark of the hatch as Petra held it open. He was going to fit, but with only a finger’s width to spare. The chute sloped away at an alarming pitch.

“I thought you said you were going to trust me.” Petra pointed into the chute.

David shut his mouth and put his head into the hatchway. He pushed farther and farther into the square metal hole, then yelped as two hands closed around his ankles and heaved. Petra’s laugh was cut off as his body filled the chute, and he was falling. He found himself hurtling down into the dark in what had to be a near-vertical drop.

In seconds he was out and facedown in a heap of dirty clothes. In the pitch black, David rolled frantically to free himself, but when he finally got the sheet off he banged his head on a low metal ceiling and fell back into the dirty linen, stunned.

It seemed to take Petra much longer than five minutes to get there, and when a doorway finally opened and that familiar tangle-haired silhouette appeared, David could tell she was still laughing.

“Come on out now,” she said. “You have passed the test.”

“Test? What test?” David asked as he crawled out of the laundry cupboard.

“You really do trust me. That was mad, what you just did,” said Petra. “But let’s not wait around here. Come.”

He followed her out of the laundry room, too glad to see her smiling again to be angry at being played with. And she had got him out of the Lodge. They moved swiftly down a corridor and then climbed two flights of stairs to the level where the canteen was. Petra ran here, silent in her boots, and David did the same. He followed her into a recess. She opened a service door at the back and they ducked through into a deep cupboard.

Petra walked straight to the back of it, pushing past mops, buckets, and brooms. In the gloom, David heard a metal panel being popped free, and weak light broke through from beyond. Behind the cupboard was a narrow rock passage that seemed prehistoric after the clean, modern surroundings of the rest of the base.

“What is this?” asked David.

“When they extended Unsleep House, they just went straight down into the mountain beneath,” said Petra. “There was a vast cavern there already, and even now there are still some unused natural passages like this one. It joins with the main tunnel entrance to the château’s cellar.”

“Is this how you get into the château normally?” said David, surprised. The only light came from a few flickering neon strips hanging from bundled cables that ran along the ceiling, and there were places where water dripped through.

“No,” said Petra, stepping into the passage. “I don’t know what this passage is, or why it is lit — it seems to have been forgotten. But this is the way I sometimes come when I want to go out.”

“Out?” said David as he followed her. They made their way along the tunnel in single file, Petra leading the way.

“Sometimes I need to be on my own,” said Petra. “Or at least not down in the base. Like your grandfather, I don’t like being cooped up underground all the time. The château is more like a real home.”

“But don’t you ever go home?” said David. “To your parents? Théo said that not all dreamwalkers live here. What about Christmas, holidays?”

Petra slowed down and then stopped walking. She stood with her back to him. David waited, wondering what he’d said. Eventually she turned.

“This is my home,” she said in a small voice. “David, I am going to tell you something, something that you will hear sooner or later. I want you to hear it from me, okay?”

“Okay.”

“When I first dreamwalked, I was only nine years old. I had no idea what was happening, of course; I thought it was just a wonderful dream. But I soon found out the truth.”

“Someone from Unsleep House came and picked you up?” said David. “They ‘activated’ you?”

Petra shook her head.

“They spotted me on the Map, but they didn’t reach me in time. Others were watching too.”

David said nothing. The air around him seemed suddenly chilly.

“The Haunting got to me first.” Petra looked at the ground. “They raided my home. I was taken.”

“Taken?” said David. “What about … ?”

“My family? The Haunting only take what they want, David, and they only want dreamwalkers. They can’t afford to leave witnesses.”

David didn’t know what to say.

“I was held for over a year,” Petra continued, forcing the emotion out of her voice. “They made me dreamwalk. They forced me to terrify people, to be a ghost. They told me my family would be hurt if I didn’t. So I became one of them.”

“You … you were a haunter?”

“Yes.” Petra’s face had disappeared behind a curtain of curls. “They told me it was my destiny, that this was what dreamwalking was really all about — being a ghost, haunting the past in order to change it. They promised me riches and power, and if I questioned them, they threatened to hurt those I love. They made me into a monster.”

“The statue! In the museum!” David said, suddenly remembering the terrifying image of the Gorgon with the snake hair and piercing eyes. “That really was you, wasn’t it?”

“That was the form they needed from me. I didn’t have any choice.”

“But you were rescued …”

“I escaped!” snapped Petra, her hair flying back so that her eyes flashed in the gloom. “I am the only one who has ever escaped from the Haunting. I drifted for a while, but then Unsleep House took me in. That’s how I found out that my family had been murdered. I did all those terrible things to protect them, but they were already gone.”

David stared. He felt numb inside.

“The King of the Haunting,” he said eventually, without really intending to say it aloud.

“Where did you hear that?”

“The professor said something about the Haunting being led by a king,” David said. “Did you … did you ever … ?”

“Meet him?” Petra’s eyes flashed again. “No, David. If only I had!” Then she spoke more coolly. “When I got here, I did all I could to destroy the Haunting; I told the professor everything I knew. But it wasn’t enough. King is just a word, after all, and no one knows what it means. So the Haunting are still free to keep doing what they do. They still take dreamwalkers as slaves. They still murder those who get in their way.”

“Petra, I’m so sorry,” said David in a whisper, “about your family.”

Petra looked at him with moist eyes.

“It is not for you to be sorry. You didn’t know,” she said.

“But I do know what it’s like to lose someone close,” said David.

“Your father. Yes.” Petra stepped closer then and took David’s hand.

“We’re dreamwalkers,” she said, looking up into his face. “Life is different for us, as you’ve seen, but death is too. When we lose someone it’s not the same as it is for other people. When someone dies they come to the end of their time, but that time — the time when they lived — is still out there somewhere. It still happened. And we are the lucky ones who can slip back and visit that time again and see those we have lost. It’s a wonderful thing we can do, David. The Haunting is wrong. This is the greatest gift of the dreamwalker.”

David blinked at her. He really hadn’t thought of it like that.

“So you do this?” he said eventually. “You visit your family as a dreamwalker?”

Petra smiled again, but her face was still sad.

“Once,” she said. “I did it once. But it was too hard. I wanted them to see me, but that would have been so wrong. How would they have reacted? How could I have explained? No. Instead I just stood there in a shadow and watched and …”

It looked to David as if she was about to cry, and he was amazed she hadn’t yet. He put his arms around her, unsure if this was really the right thing to do, or if he was allowed. Petra accepted his touch for a moment, but then gently pushed him away.

“It’s okay,” she said. “I’m okay.”

They looked at each other for a moment.

“I don’t need to see my family again,” she said, “not like that. But knowing that I could visit them, that they are still out there somewhere, happy and unaware in their own time, that’s a great comfort. You might find it a comfort also.”

David put his hands in his pockets and looked at the floor. Part of his mind was dealing with the unexpected thought that he could see his father again, in a sense. But another part of it was thinking of Petra and how close she was standing. Then she spoke again and broke the strange moment.

“You will find that some on the Dreamwalker Project still don’t trust me. You heard what Roman said in the Archive — once a haunter, always a monster, that’s what they think. I just wanted you to know the truth from me before you hear any stories, that’s all. Now let’s go find your grandfather’s study. Come.” She turned on her heel and set off down the corridor again.