Fate dealt Stanley Picker a strange card that day: he just happened to be ambling past the burning library on his way home from work as the rampaging mob surged out into the street pushing trolleys of rare books and manuscripts.

Amidst all this mayhem, Stanley only had eyes for the odd little cipher manuscript balanced precariously on top of one of the piles of books being noisily wheeled past him. He could not possibly have known that it was better known as “MS 666”, nor that the library had marked it down as a “shorthand diary” (nor how strangely correct this was); nor indeed could he have known that its provenance led back through Aleister Crowley (yes, the Great Beast himself) and onwards to dark places heaven (or perhaps hell) only knows.

Though at that precise moment Stanley believed he was picking up the book, who can say for certain that in some hard-to-fathom fashion it was not in fact picking him up? In the way that Marxist historians insist that factory machinery consumes the workers that operate it, do not cipher mysteries similarly consume the historians, researchers and other passing fools who apply themselves to their unfathomable challenges? It could be said that poor Mr Picker was not really the picker: rather, the small book was pursuing its own dangerous agenda, one to which he was quite oblivious.

And so it was that, with the swiftest of surreptitious shuffles, the tiny volume silently disappeared under Stanley’s work coat. Now it would be free, far from the tyranny of the library’s dull lighting and (surely its #1 pet hate) that bow-tied moron Edward Jackinder with his narrow eyes and scratchy facial hair who kept trying to decipher it.

Back at his house, Stanley opened out his new-found meta-linguistic trophy on the kitchen table and started to examine it. School had left him not only with a profound distrust of gym teachers but also with reasonably functional Maths and language skills: so it didn’t take him long to realize that his prize appeared to be written in an unknown European language (though admittedly one all of its own).

But the strangest thing about it was that every time he returned to its final page, there appeared to be slightly more text. At first, he of course thought he might have been mistaken, but as the days crawled by, the writing gradually reached the bottom and started at the top of the next one. He found himself talking to the diary, trying to verbalize both his curiosity and his growing unease with its ongoing metamorphosis: his mornings now brought crippling headaches, stopping him from going into work.

At the same time, Jackinder was grimly pursuing the book’s smokey trail: though he could make out the thief’s jacket on the CCTV footage, and had worked out where the man must work, nobody at that supermarket seemed able to identify him from the images. It was almost, he mused, as if the man was being silently erased, painted out of the picture one obscuring daub at a time.

But a few weeks later, Jackinder caught sight of him buying milk in a corner shop not far from the library. In a strange way his face had become thinner, much greyer since the theft – but the resemblance was unmistakeable, beyond any shadow of a doubt. Deliberately putting down his basket, Jackinder narrowed his eyes even more than usual and resolved to follow and confront this wretched criminal.

Yet the two didn’t have far to go to reach the flat marked “S. Picker”: and as the man stumbled up his steps, almost fell over the threshold to the house, and left the front door wide open behind him, Jackinder knew something was badly wrong. Hesitantly, he followed him inside the open plan apartment, finding Stanley laying on the sofa near-dead and – mirabile dictu, his heart wanted to shout – MS 666 open on the kitchen table, its pages turning lightly in a late Summer breeze. Yet… what was this madness? The ill-looking thief had apparently vandalized the manuscript, even adding his own fake cipher text to the final page. That was wrong on so many levels, he mused: really, what kind of an idiot would do such a thing?

This wasn’t really going to plan, Jackinder thought to himself as he slowly straightened up. In his mind’s eye, he had simply intended to wield the mighty sword of academic righteousness, by finding this stolen book and returning it triumphantly to the library. As he stood there holding MS 666 in his very own hands, the problem was that he now realized that he had quite another option – to take it for himself. Picker was lying there in pain, utterly unaware that Jackinder had even entered the flat behind him: Jackinder could do precisely what he liked, and nobody need ever know.

Slowly, almost unwillingly, Jackinder felt his hands sliding the book inside his jacket, and his feet walking slowly out through the door and down the street. He didn’t know where he was going or even why, but a strange new sense of purpose – an almost deadly elation, in fact – was consuming him, driving him ever forward.

He could not possibly have known, but the further Jackinder walked, the more writing was now appearing inside MS 666: but this time it was not just a single page, but a whole new chapter.