I drove to St Helier and the Library of the Museum of the Société Jersiaise. They said it was private but I murmured the name of a learned Rector and, instantly, red carpets blossomed beneath my feet.

The material I wanted was dispersed and hard to find, for I particularly did not want to enlist the librarian’s help, and, when I found it, a great deal was in Patois Jersiais and the rest in antique Norman-French. A sample of Patois will, I think, give you an idea of the horrors of that tongue: ‘S’lou iou que l’vent est quand l’soleit s’couoche la séthée d’la S. Miché ché s’la qu’nous etha l’vent pour l’hivé.’ This is supposed to mean that the direction of the wind at sunset on Michaelmas Day will be the prevailing wind throughout the following winter – a likely story, I must say.

I staggered out into the evening sunshine and the monstrous regiment of tourists with my head buzzing-full of recondite information. It was clear that scholarship of that kind was not for Mortdecai: a specialist was called for. Nevertheless, I now knew a few things about Paisnel which the police didn’t. For instance, both he and his china toad had indeed been ‘part of something’; something which is supposed to have died three hundred years ago, something almost as nasty as the people who stamped it out – or thought they had.

Johanna was out when I arrived at the flat; she would be playing bridge, the least strenuous of her vices, bless her. With luck she would get home very late and too tired for romps.

I wrote to Hatchards for a copy of Malleus Maleficarum, that great compendium of medieval horrors, and begged them, with many an underlining, to see that it was in English.

Jock and I, on friendly terms again, feasted in the kitchen on pork chops, fried peas and mashed potatoes, capping them with a croque-monsieur in case of night starvation.

Then, aiding digestion with a bottle of Mr Teacher’s best and brightest, we watched Bogart and Bergman in Casablanca, that flawless pearl of a film. There wasn’t a dry eye in the house. If television didn’t exist, someone would have to invent it, is what I say.

I was in hoggish slumber when Johanna climbed into my bed, she was glowing with the radiance of a woman who has just won more than eighty pounds from a close friend. She spends at least that sum each month on her breakfast champagne but her pleasure was intense and she tried to communicate it to me in her own special way.

‘No, please,’ I protested, ‘it’s very late and I am suffering from Excess at Table.’

‘Well at least tell me what happened today,’ she pouted. ‘Did you catch the Fiend in Human Shape?’