‘Your most serious mistake was in killing that witch,’ the Spook said. ‘She should have been brought back here. Mother Malkin is so strong that she could even break free of her bones. It’s very rare but it can happen. Her spirit could be born into this world again, complete with all her memories. Then she’d come looking for you, lad, and she’d want revenge.’

‘That would take years though, wouldn’t it?’ I asked.

‘A newborn baby can’t do much. She’d have to grow up first.’

"That’s the worst part of it,’ the Spook said. ‘It could happen sooner than you think. Her spirit could seize someone else’s body and use it as her own. It’s called "possession" and it’s a bad business for everybody concerned. After that, you’ll never know when, and from which direction, the danger will come.

‘She might possess the body of a young woman, a lass with a dazzling smile, who’ll win your heart before she takes your life. Or she might use her beauty to bend some strong man to her will, a knight or a judge, who’ll have you thrown into a dungeon where you’ll be at her mercy. Then again, time will be on her side. She might attack when I’m not here to help -maybe years from now when you’re long past your prime, when your eyesight’s failing and your joints are starting to creak.

‘But there’s another type of possession – one that’s more likely in this case. Much more likely. You see, lad, there’s a problem with keeping a live witch in a pit like that. Especially one so powerful who’s spent her long life practising blood magic. She’ll have been eating worms and other slithery things, with the wet constantly soaking into her flesh. So in the same way that a tree can slowly be petrified and turned into rock, her body will have been slowly starting to change. Gripping the rowan staff would have stopped her heart, pushing her over the barrier into death, and being washed away by the river might have speeded up the process.

‘In this case, she’ll still be bound to her bones, like most other malevolent witches, but because of her great strength she’ll be able to move her dead body. You see, lad, she’ll be what we call "wick". It’s an old County word that you’re no doubt familiar with. Just as a head of hair can be wick with lice, her dead body is now wick with her wicked spirit. It’ll be heaving like a bowl of maggots and she’ll crawl, slither or drag herself towards her chosen victim. And instead of being hard, like a petrified tree, her dead body will be soft and pliable, able to squeeze into the tiniest space. Able to ooze up someone’s nose or into their ear and possess their body.

‘There are only two ways to make sure that a witch as powerful as Mother Malkin can’t come back. The first is to burn her. But nobody should have to suffer pain like that. The other way is too horrible even to think about. It’s a method few have heard about because it was practised long ago, in a land far away over the sea. According to their ancient books, if you eat the heart of a witch she can never return. And you have to eat it raw.

‘If we practise either method, we’re no better than the witch we kill,’ said the Spook. ‘Both are barbaric. The only alternative left is the pit. That’s cruel as well, but we do it to protect the innocents, those who’d be her future victims. Well, lad, one way or the other, now she’s free. There’s trouble ahead for sure, but there’s little we can do about it now. We’ll just have to be on our guard.’

‘I’ll be all right,’ I said. ‘I’ll manage somehow.’

‘Well, you’d better start by learning how to manage a boggart,’ the Spook said, shaking his head sadly.

‘That was your other big mistake. A whole Sunday off every week? That’s far too generous! Anyway, what should we do about that?’ he asked, gesturing towards a thin plume of smoke that was still just visible to the south-east.

I shrugged. ‘I suppose it’ll be all over by now,’ I said. ‘There were a lot of angry villagers and they were talking about stoning.’

‘All over with? Don’t you believe it, lad. A witch like Lizzie has a sense of smell better than any hunting dog. She can sniff out things before they happen and would’ve been gone long before anyone got near. No, she’ll have fled back to Pendle, where most of the brood live. We should follow now, but I’ve been on the road for days and I’m too weary and sore and need to gather my strength. But we can’t leave Lizzie free for too long or she’ll start to work her mischief again. I’ll have to go after her before the end of the week and you’ll be coming with me. It won’t be easy but you might as well get used to the idea. But first things first, so follow me…’

As I followed, I noticed that he had a slight limp and was walking more slowly than usual. So whatever had happened on Pendle, it hadn’t been without cost to himself. He led me into the house, up the stairs and into the library, halting beside the furthest shelves, the ones near the window.

‘I like to keep my books in my library,’ he said, ‘and I like my library to get bigger rather than smaller. But because of what’s happened, I’m going to make an exception.’

He reached up and took a book from the very top shelf and handed it to me. ‘You need this more than I do,’ he said. ‘A lot more.’

As books went it wasn’t very big. It was even smaller than my notebook. Like most of the Spook’s books, it was bound in leather and had its title printed both on the front cover and on the spine. It said: Possession: the Damned, the Dizzy and the Desperate.

‘What does the title mean?’ I asked.

‘What it says, lad. Exactly what it says. Read the book and you’ll find out.’

When I opened the book, I was disappointed. Inside, every word on every page was printed in Latin, a language I couldn’t read.

‘Study it well and carry it with you at all times,’ said the Spook. ‘It’s the definitive work.’

He must have seen me frowning because he smiled and jabbed at the book with his finger. ‘Definitive means that so far it’s the best book that’s ever been written about possession, but it’s a very difficult subject and it was written by a young man who still had a lot to learn. So it’s not the last word on the subject and there’s more to discover. Turn to the back of the book.’

I did as he told me and found that the last ten or so pages were blank.

‘If you find out anything new, then just write it down there. Every little bit helps. And don’t worry about the fact that it’s in Latin. I’ll be starting your lessons as soon as we’ve eaten.’

We went for our afternoon meal, which was cooked almost to perfection. As I swallowed down my last mouthful, something moved under the table and began to rub itself against my legs. Suddenly the sound of purring could be heard. It gradually got louder and louder until all the plates and dishes on the sideboard began to rattle.

‘No wonder it’s happy,’ said the Spook, shaking his head. ‘One day off a year would have been nearer the mark! Still, not to worry, it’s business as usual and life goes on. Bring your notebook with you, lad, we’ve a lot to get through today.’

So I followed the Spook down the path to the bench, uncorked the bottle of ink, dipped in my pen and prepared to take notes.

‘Once they’ve passed the test in Horshaw,’ said the Spook, starting to limp up and down in front of the bench, ‘I usually try to ease my apprentices into the job as gently as possible. But now that you’ve been face to face with a witch, you know how difficult and dangerous the job can be and I think you’re ready to find out what happened to my last apprentice. It’s linked to boggarts, the topic we’ve been studying, so you might as well learn from it. Find a clean page and write down this for a heading…’

I did as I was told. I wrote down, ‘How to Bind a Boggart amp;rsquo.; Then, as the Spook told the tale, I took notes, struggling to keep up as usual.