‘Very well,’ I said at length. ‘We’ll give the Satanic Mass a crack of the whip; I’m sure you know best.’

‘Capital, capital; I always said that you were a capable man. I remember saying so to the Dean when – ’

‘Yes, John. Now, how does one go about arranging that sort of beano?’

‘Of course, let us be practical. First, we must select a suitable Mass. What? Oh, goodness, yes, there are many. Many. By far the best is the Medici Mass, it never fails, it is positively and finally lethal, but there are no reliable texts of its Graduale to be had – all corrupt, every one of them, such a shame. In any case, the Missa Mediciensis involves the dismemberment of a beautiful young boy, which I fancy you might think a horrid waste – or am I thinking of a chap with a name like yours who came up in the same year as you?’

‘Bonfiglioli?’ I asked.

‘Yes, that was he. Sorry, Mortdecai. And in any case, unless your Jersey witchmaster is uncommonly learned he may not have heard of that particular ritual and it is of the greatest importance that he should know what forces you are throwing against him. You see that, don’t you?’

‘It makes sense, certainly.’

‘Ah. Yes. Now I have it: the very one, the Messe de Saint Sécaire.’

‘And who, pray, was Saint Sécaire?’

‘Well, he probably wasn’t a saint; in fact he may never have been what you or I would call a person even, but his name is known everywhere from the Basque country to the Lowlands-Low amongst the sort of people who know about that sort of thing.’

‘You speak in riddles, John.’

‘Naturally. Now, you will need only three things: first, an unfrocked priest, for the ritual demands it. I know the very chap: he teaches in a prep-school in Eastbourne and is both reliable and cheap. It will only cost you his steamer-fare – chaps like that never travel by air for obvious reasons – and a few bottles of Pastis; some clean straw to sleep-it-off on and perhaps a couple of flyers as a going-away present.’

‘I have a servant called Jock who will anticipate his every need.’

‘Splendid. Then, you will need a text of the Ritual. There is only one sound copy in existence: it is in the incomparable library of a ridiculous old lecher called Lord Dunromin. I shall give you a letter to him: if you grovel a bit and pretend to believe that he is – as he loves to think – the wickedest man in England, he may be persuaded to let you have a sight of the manuscript and copy out such parts as differ most grossly from the Ordinale. Pay particular attention to the peculiarities of the Introit, the Kyrie and the, well, the equivalent of the Agnus Dei.’

I scribbled some notes on my shirt-cuff, for I knew that such an anachronism would please him.