Detective Inspector Thomas Nightingale is my boss, my governor and my master – purely in the teacher–pupil teacher sense of the term, you understand – and on Sundays we generally have an early dinner in the so-called private dining room. He’s a shade shorter than me, slim, brown hair, grey eyes, looks forty but is much, much older. While he doesn’t routinely dress for dinner he always gives me the strong impression that he only holds back out of a courtesy to me.

We were having pork in plum sauce, although for some reason Molly felt that the ideal side dish was Yorkshire pudding and cabbage sautéed with sugar. As usual Lesley chose to eat in her room – I didn’t blame her; it’s hard to eat a Yorkshire pud with dignity.

‘I’ve got a little jaunt into the countryside for you tomorrow,’ said Nightingale.

‘Oh yeah?’ I asked. ‘Where to this time?’

‘Henley-on-Thames,’ said Nightingale.

‘What’s in Henley?’ I asked.

‘A possible Little Crocodile,’ said Nightingale. ‘Professor Postmartin did a bit of digging for us and uncovered some additional members.’

‘Everybody wants to be a detective,’ I said.

Although Postmartin, as keeper of the archives and old Oxford hand himself, was uniquely suited to tracking down those students we thought might have been illegally taught magic. At least two of these had graduated to total bastard evil magician status, one active back in the 1960s and one who was alive and well and had tried to knock me off a roof back in the summer. We’d been five storeys up so I took it personally.

‘I believe Postmartin has always fancied himself as an amateur sleuth,’ said Nightingale. ‘Particularly if it’s largely a matter of gathering university gossip. He thinks he’s found one in Henley and another residing in our fair city – at the Barbican no less. I want you to drive up to Henley tomorrow and have a sniff around, see if he’s a practitioner. You know the drill. Lesley and I shall visit the other.’

I mopped up the plum sauce with the last of my Yorkshire pudding. ‘Henley’s a bit off my patch,’ I said.

‘All the more reason for you to expand your horizons,’ said Nightingale, ‘I did think you might combine it with a “pastoral” visit to Beverley Brook. I believe she’s currently living on that stretch of the Thames.’

On the Thames, or in it? I wondered.

‘I’d like that,’ I said.

‘I thought you might,’ said Nightingale.