What amazes me most about this modern world is that people aren't more amazed. I first lived in a time of magic, with priestesses and druids who could perform wondrous feats. But we had nothing like aeroplanes, computers, televisions, cars. We were servants of the natural world, ignorant of the ways of the universe and the origins of our planet. We didn't even know the Earth was round!

Today's people have mastered the land and seas, and even made inroads into the heavens-they can fly! There are things they can't control, like earthquakes and floods, but for the most part they've torn down trees, carved the planet up with roads and made it theirs. They've hurt the Earth, and they don't seem as happy as people in my time were, but they've achieved the incredible.

I've been here more than six months, yet I still find a dozen things each day that make my jaw drop. Like a pencil. How do they put lead inside wood? And paper-nobody thinks twice about it, but in my previous life, if you wanted to record a message, you had to hammer notches out of a chunk of rock.

It's a terrifying world and I shouldn't be able to cope with it. I came back to life as a small, scared, lonely girl. If I'd stepped out of the cave knowing nothing of what lay beyond, I'd have fainted with shock and gone on fainting every time I recovered and looked around.

But when I took over Bill-E Spleen's body, his memories became mine. It took me a few weeks to process everything, but I soon knew all that he did. That helped me make sense of this new world and deal with it. Without access to Bill-E's memories I wouldn't have known how to use a knife and fork, knot a pair of laces, open a door or do any of the simple, everyday tasks that everyone else takes for granted.

But as helpful as that's been, it's also proved to be one of my biggest problems. Because I live with Bill-E's uncle, Dervish Grady, and I made the mistake of telling him about Bill-E's memories. As a result, he sees me as some kind of a medium, offering him unlimited access to his dead nephew's feelings and thoughts.

"Tell me about Billy's first day at school."

We're in Dervish's study on the top floor of the house. The mansion is a three-storey monster, full of round, stained-glass windows, wooden floorboards and bare stone walls. (Except in this study, which is lined with leather panels.) All of the people from my village could have lived in comfort here. When I first saw it, I thought it was a communal building.

"His first day at school?" I chew my lower lip, as though I have to think hard to retrieve the memories. Dervish watches me intently, hands crossed on the desk in front of him, eyes hard. I don't enjoy these sessions. He brings me up here three or four times a day and asks me about Bill-E, the things he experienced, the thoughts he had, the way he saw the world.

"He wasn't nervous," I begin. "He thought it was a big adventure. He loved putting on his uniform and packing his books and lunch. He kept checking the kitchen clock, even though he couldn't tell the time."

Dervish smiles. He always grins when I tell him an amusing little detail about his dead nephew. But he's not smiling at me-he's smiling to himself, as if sharing a joke with the absent Bill-E Spleen.

I tell Dervish more, talking him through the young boy's impressions of his teacher and classmates. I find this boring as well as uncomfortable. It's like having to read chapters from the same story, over and over. My attention wanders and my eyes dart round Dervish's study, the books of magic on the shelves, the weapons on the walls. I want to flick through the pages of those books and test some of the axes and swords. But there's never time for that.

Maybe Dervish doesn't see me. Perhaps to him I'm not a real person, just a mouthpiece for Bill-E. I doubt that he can imagine me doing anything other than talk about the boy I replaced. There's nothing malicious in it. I just don't think it's crossed his mind to regard me as an independent human being.

Eventually, two hours later, Dervish dismisses me. He's had enough for now. He waves me away, not bothering to even say goodnight. I leave him staring at his crossed hands, thoughts distant, a sad wreck of a man, more lost in the past than I ever was when captive in the cave.

I love walking, exploring the countryside between the house and Carcery Vale. I like it in the forest. The land was covered in trees when I first lived. I almost feel like I'm in my original time when I leave the roads and paths of the modern world and stroll through woodland. Sometimes I'll pluck a leaf and set it on my tongue, to taste nature. I try to trick myself into believing the new world doesn't exist, that the natural balance has been restored.

Of course that's fantasy and the sensation never lasts long. These trees have been carefully planted and the undergrowth is nowhere near as dense as it was back then. There are still rabbits and foxes, but they're scarce.

No wolves or bears. The smell of the modern world is thick in the air, a nasty, acidic stench. But if I use my imagination, I can believe for a second or two that I'm in the forest near my rath.

Sometimes, in the night, I truly forget about the present. In my dreams I'm still Bec MacConn, learning the ways of magic from my teacher, Banba. I wake up in a cold sweat, heart racing, crouched close to the wall, wondering where I am, why there's a hole in the wall and what the clear, hard material stretched across it is. I feel trapped, as if I'm back in the cave. I swipe my fists at imagined phantoms of this new, scary world.

The confusion always passes swiftly. After a minute or two I remember where and when I am. My fists unclench and my heart settles down. I find it hard to sleep again on such nights, and lie awake in the dark, often curled up on the floor in a corner, remembering those I knew, all long dead and decayed. I feel lost and alone on such nights, and tears often fall and soak my cheeks as I tremble and miserably hug myself.

But it's day now and I feel more relaxed. I move through the forest, humming a tune the world hasn't heard in more than a millennium, pretending that I'm back in my own time. I come to a bush of red berries. I'm reaching for a berry to examine it when I spot a car and realise I'm close to a road. I still feel uneasy around cars, even after six months. I haven't been in one yet, although I've been on Dervish's motorbike a couple of times, when he took me to a nearby town to get clothes.

Cars frighten me. They look vicious. Growling, screeching, fast-moving assassins. I know they're not living, thinking creatures, but I can't help myself. Whenever I see a car, I expect it to race after me, chase me through the trees and mow me down.

I wait for the noise of the engine to fade, then edge over to the road. I've explored all the area around Dervish's home and can pinpoint my position within half a minute, no matter where I am. One look at the road, the trees by its side and the bend to my left, and I know I'm a five-minute walk from Carcery Vale, the nearest village.

I haven't been to the Vale often. The people there make me nervous. I keep quiet and don't interact with them. I feel out of place, afraid I'll say something to give myself away. I'm not truly part of this world and I can't shake the feeling that our neighbours will eventually unearth my secret.

My first week here was mad. We'd just saved the world from a demon invasion, but there was no time to take pride in our achievement. Beranabus-as Bran now calls himself-left the day after our showdown with Lord Loss. We'd glimpsed the demon master's superior in the cave-a huge, mysterious, shadowy, powerful beast. Lord Loss said our hours were numbered, that we'd only delayed the day of reckoning.

Beranabus was overwhelmed by my reappearance. I was the only person he'd ever cared about, and my return brought happiness back into his life. But the ancient magician is practical above all else. He wanted to stay and spend his last few years by my side. But there were demons to fight and a world to save. There was no time for selfish pleasure.

He took his assistant, Kernel Fleck, and Grubbs Grady-another of Dervish's nephews-with him. Grubbs is very powerful, but he hates fighting demons. He'd spent his life hiding from his responsibilities, but Bill-E's death seemed to settle him on his path. As reluctant as he was to leave Dervish, as scared as he was to face the Demonata, he went anyway.

Beranabus should have taken me too. When Grubbs, Kernel and I unite, we become the Kah-Gash. We have the power to destroy a whole universe. Beranabus should have kept us together, to experiment and use us.

He left me behind for two reasons. The first was personal. I'd suffered sixteen hundred years of imprisonment and he didn't want to thrust me into the demon's universe to fight immediately. He felt I deserved a few years of peace and wished to spare me the awfulness of my destiny as long as he could.

But he was scared as well, and that was the main reason. Beranabus had been searching for the Kah-Gash most of his life, hoping to destroy the Demonata with it. But he'd never been sure if he was chasing a mythical Holy Grail or an actual weapon. When he saw it in action, doubt crept in.

Was he right to put the pieces together? What if we fell into the hands of the Demonata and they used us to annihilate the human world? Or maybe the Kah-Gash would work against us by itself. We hadn't intentionally taken the universes back in time. The Kah-Gash did that, having manipulated Grubbs into helping the demons open the tunnel in the first place. It had a mind and unknowable will of its own. Perhaps it had saved us by accident.

Wary of the weapon, Beranabus split us up. He should have left Grubbs behind to comfort Dervish, and he would have if not for his love of me. Dervish went into a rage when he woke to be told Grubbs had slipped away in the middle of the night. Grubbs and Bill-E were his nephews, but they'd been like sons. Now he'd lost them both. He cursed Beranabus, the demons... and me. He blamed me for Bill-E's death, accused me of conspiring against the boy, tricking him so that I could take over his body.

It was the first day of my new life. Everything was confusion and uncertainty. I was awestruck, afraid, not sure what to say or how to act, delighted to be alive, but terrified. Unsure of myself, I let Dervish curse and scream. I didn't flinch when he jabbed a finger at me or lifted me off the ground and shook me hard, only prayed to the gods that he wouldn't kill me.

In the end he stormed off. He ignored me for days, and would have ignored me for longer- maybe forever-if not for Meera Flame, one of his oldest friends. In the middle of his depression, he rang her to tell her about his loss. Meera came to him immediately. After doing what she could to console Dervish, she asked if I needed anything, if I wanted to talk about what I'd been through.

Meera was wary of me. Like Dervish, she wondered if I'd led Bill-E to his death, so that I could take control of his body. Through floods of tears I convinced her of my innocence. When she realised I was just a lonely girl, as scared of this new world as I was of demons, her heart warmed to me and we were able to talk openly. I told her about my life, my centuries in the cave, the force which compelled me to take Bill-E's body.

"I didn't want to bring the corpse back to life and change it," I sobbed. "It just happened. It was lying there, good for nothing else, and I had the power to make it mine. In those first few minutes, I wasn't thinking about living again. I could see that Lord Loss was going to kill the others. I just wanted to help them."

Meera believed me and managed to convince Dervish of the truth. She also dealt with the difficulties of Bill-E's disappearance and my sudden existence. She got Dervish to pretend Bill-E had gone to live with relatives. Through her contacts, Meera faked the necessary paperwork and arranged for officials in high positions to throw their weight behind the lie if anyone (such as Bill-E's teachers) made enquiries.

Those same contacts forged a birth certificate and passport for me. I became an illegitimate niece of Dervish's, whose mother had recently passed away. In the absence of any other living relative, I'd been sent to Carcery Vale.

It was too coincidental to pass close scrutiny. A boy's grandparents are brutally slaughtered... the boy takes off without saying a word to anyone... his best friend also disappears... and a girl nobody has ever heard of moves in with the man who was like a father to both boys. The people of Carcery Vale aren't stupid. I'm sure they knew something was wrong.

But Meera and her allies covered their tracks artfully. Police were assured by their colleagues in other districts that Bill-E was safe and the girl's story was on the level. In the face of such carefully contrived evidence, our neighbours could do nothing except watch suspiciously and wait for the next bizarre Grady family twist.