The General Library is where me and Lesley do most of our studying. It’s got a couple of ornate reading desks with angular brass reading lamps and an atmosphere of quiet contemplation that is totally spoiled by the fact that we both have our headphones on when we’re studying.

Nightingale strode over to the shelves that I’d come to know as the eccentric naturalist section. He tapped his finger along a line of books before pulling one out and inspecting it. ‘Jules Barbey d’Aurevilly is probably the authority,’ he said. ‘How’s your French?’

‘Do me a favour,’ I said. ‘I’m barely keeping up with my Latin.’

‘Pity,’ said Nightingale and replaced the book. ‘We should get that translated one day.’ He pulled out a second, thinner, volume. ‘Charles Kingsley,’ he said and handed the book to me. It was titled On Fairies and Their Abodes.

‘Not as comprehensive as Barbey d’Aurevilly,’ said Nightingale. ‘But reasonably sound, or at least so my tutors assured me when I was at school.’ He sighed. ‘I did prefer things when we all knew what we were doing and why.’

‘Before I ran into Zach I ran into Fleet,’ I said. ‘And before I ran into Fleet I ran into a Chinese woman who I’m pretty sure was a practitioner.’

‘Did she introduce herself?’

I told him all about the mysterious Madame Teng, although I left out the fact that I’d essentially been rescued by Fleet and her Captain of Dogs.

‘Good god, Peter,’ said Nightingale. ‘I can’t leave the city for five minutes.’

‘Do you know who she was?’ I asked.

‘A Daoist sorceress I would imagine,’ said Nightingale.

‘Is that good or bad?’

‘The Chinese have their own traditions, including the practice of magic,’ said Nightingale. ‘As I understand it, Daoist magic is based on writing characters on paper much in the same way that we speak formae aloud. Beyond that I don’t think we ever discovered how it works. Contact was limited, we didn’t want to tell them our secrets and unsurprisingly they didn’t want to share theirs with us.’

He frowned at the bookcase and swapped two volumes around.

‘Do they operate out of Chinatown?’ I asked.

‘We have an arrangement with Chinatown,’ he said. ‘They don’t scare the horses and we don’t go in asking questions. Mao pretty much killed all the practitioners during the 1950s and any that survived on the mainland were finished off in the Cultural Revolution.’

‘She was from Taiwan,’ I said.

‘That would make sense,’ said Nightingale. ‘I’ll look into it.’

Just to make Nightingale’s day I finished off with a description of Ryan Carroll’s – possibly – magical art installation.

‘And there I was hoping that we could leave that case to the Murder Squad and concentrate on the Little Crocodiles,’ said Nightingale.

‘Anything useful in Henley?’ I asked.