As I leaned over the bannister and peered into the inky depths of Hogwarts, I couldn't help feeling that of all the half-baked schemes I had ever got mixed up in, this one was the most half-baked by a country mile. And that's saying a lot. As my regular readers will know, I am hardly a wet-behind-the-ears novice when it comes to skulduggery in the lonely watches of the night. I mean, study the history books. There was the time at Totleigh Towers when, for reasons too complicated to be expounded upon here, I had to tiptoe downstairs in the wee hours of the morning in order to steal a cow-creamer, and there was the other time at Steeple Bumpleigh when, armed with treacle paper and half a brick, I had to lurk around in the garden after nightfall, waiting for the opportunity to smash a downstairs window.

So, as I say, I'm no rookie in these matters. But I don't think I exaggerate when I say that having to creep down to the dungeons of Hogwarts castle at dead of night, in order to nab the philosopher's stone before anyone else could lay their hands on it, was the scaliest challenge that Bertram Wooster had ever faced. I didn't like it one bit.

'Jeeves,' I said, when that good fellow had materialised at my side. 'Who was that chap who peered deep into the darkness, and stood there fearing, and so on?'

'I believe you allude to the poem entitled The Raven, Sir, by Edgar Allan Poe. "Deep into that darkness peering," it says, "long I stood there, wondering, fearing, doubting, dreaming dreams no mortal ever dared to dream before.'

'Well, except for the part about dreaming, that's exactly how I feel,' I said, and I might have elaborated on the matter, but, even as I continued peering, my mind moved on to more practical matters. 'At a rough estimate, Jeeves, how many staircases would you say there are between this floor and the dungeons?'

'Thirteen, Sir.'

'Thirteen?'

'I believe so, Sir.'

'All of them in working order?'

'Yes, Sir.'

'I bet they're not. You know what the staircases are like at Hogwarts. Each is worse than the last. Isn't there one which only opens for business on a Wednesday?'

'It is Wednesday, Sir. I trust you will be able to negotiate it without difficulty.'

'If you say, Jeeves. Personally, I take a dim view of the entire matter. I regard the whole thing as nothing more than a disaster in waiting.'

'It is often that way at the start of an adventure, Sir, but I am sure you will enjoy it once you have got into the swing of it.'

'Don't talk rot, Jeeves. Enjoy it? Pshaw! The only thing I shall enjoy, is being safe and sound in my bed again with the covers pulled over my head.'

I spoke moodily, and who can blame me? The more I looked at the plan, the less I liked it.

I mean, I don't know if you've ever stayed at Hogwarts, but if you have, you'll know that the place is absolutely heaving with ghosts. There are dozens of them, each more ghoulish than the last. There's one whose idea of a joke is to creep up behind you and blow in your ear and then cackle manically while you leap about twenty-five feet into the air; and there's another who goes around with his head nearly cut off but not all the way, so he looks like a tin of fruit that somebody has opened but decided not to eat at the last moment. Even worse than the ghosts are Filch, the crusty caretaker, and his cat Mrs Norris, as scaly a four-legged fiend as ever stalked the corridors of a school with padded claw and gleaming eye. Add to these the possibility of running into snooping teachers and over-zealous prefects, most of whom, one way or another, have it in for Wooster, B. and you will understand why I was not at my chirpiest.

There was gentle cough beside me. 'The invisibility cloak, Sir.'

I came out of my reverie. 'The what, Jeeves?'

'The invisibility cloak, Sir. May I suggest you put it on without further delay.'

'Very well,' I sighed, looking around for the thing. 'Where is it?'

'I am holding it in my hands, Sir.'

'Ah, that's why you're standing like that, is it? I thought you were about to play charades. Bung it over me, then.'

He did so, and spent a few moments fussing around with it — tweaking it here, smoothing it out there — before stepping back to admire the effect.

'It is working?' I asked.

'Yes, Sir, except that heel of your left shoe is still visible.'

I made the necessary adjustment myself. 'There?'

'Thank you, Sir. That has achieved the desired effect. I forget to mention, however, that while I was putting on the cloak, I noticed that your tie needs some attention. It was tending a little towards the left.'

This was too much. 'Dash it, Jeeves, I'm wearing an invisibility cloak! Who cares about ties? How can a tie, whether tending to the left or to the right, possibly matter at a time like this? I am going to steal a philosopher's stone, not attend a society ball or soiree.'

'Gentleman often find that the mere knowledge they are properly dressed, even when there are no observers, has a beneficial on the morale. My uncle Herbert…'

'Right ho, Jeeves.'

'Very good, Sir.'

'Save your Uncle Herbert for my return, what? As for my morale, nothing could have a beneficial effect on it at this moment other than someone coming and telling me the whole thing's off.'

'Very good, Sir. Unless there's anything else,' he added, 'may I suggest you make a start now. It is nearly one o'clock.'

'I suppose I had better.' I peered again over the bannister and down into the fathomless depth of the castle, and, as I did so, felt a great pang of loneliness. I turned to the man with a pleading look. Little good it did, of course, because he couldn't see me. 'Are you sure you can't come with me, Jeeves?'

'I do not think it would be wise, Sir. The cloak can only provide a satisfactory degree of invisibility to one person. However, I am sure you will be able to carry out the mission admirably by yourself.'

'That's more than I know,' I said. 'Very well, Jeeves. Don't wait up for me, but before you lay the weary head, would you be so good as to place beside my bed a large b and s? I have a feeling I shall need it on my return.'

'I shall see to it now, Sir.'

'Thank you, Jeeves. Good night, then,' I said. And without another word I slipped off along the corridor, feeling like one of those spy chappies who are sent into enemy territory armed with nothing more than an encoder ring and a cyanide pill. Except I didn't have a cyanide pill. As I descended the first of the creaking staircases and heard from somewhere a ghastly screech which may or may not have been an owl, I began to feel like I could have done with one, just in case.