She showed me the treatment bay where it happened, a white and beige cubicle with an examination bed and a curtain for privacy. The vestigium – note that I’m using the singular here – slapped me in the face as soon as I walked in. Violence, laughter, dried sweat and leather. It was the same as poor William Skirmish when he was lying in the mortuary, only minus the annoying yappy dog.

Two months previously I would have walked into that treatment bay, shivered, thought, ‘That’s weird’ and walked right back out again.

Beverley stuck her head in and demanded to know whether I’d found anything.

‘I need to borrow your phone,’ I said.

‘What happened to yours?’ she asked.

‘I blew it up in a magic accident,’ I said. ‘Don’t ask.’

Beverley pouted and handed over a surprisingly chunky Ericsson. ‘You have to top it up,’ she said. The casing had latex seals and the buttons were large and protected by a layer of clear plastic. ‘It’s designed to go underwater,’ she said. ‘Don’t ask.’

‘Can you get your acolyte to find out Dr Framline’s address for me?’

Beverley shrugged. ‘Sure,’ she said. ‘And remember, you talk, you pay!’

While Beverley was distracted with her task I took her phone outside to Beaumont Place, a quiet pedestrianised road that ran between the old and the new bits of the hospital, and called Nightingale. I described the incident and the vestigium and he agreed that it was worth stepping up the search for the courier.

‘I want to keep an eye on the doctor,’ I said.

‘Interesting,’ said Nightingale. ‘Why?’

‘I’m thinking of the sequence of events around Skirmish’s murder,’ I said. ‘Toby bites Coopertown on the nose, that’s when it starts. But Coopertown doesn’t go postal until later when he runs into Skirmish in Covent Garden.’

‘You think it was set off by a chance meeting?’

‘That’s just it,’ I said. ‘Lesley says that the Murder Team haven’t found a reason for Skirmish even to be in Covent Garden that night. He gets a bus down to the West End, meets Coopertown and gets his head knocked off. No meetings, no friends – nothing.’

‘You think both parties were affected?’ asked Nightingale. ‘You think an outside agency made them meet?’

‘Is such a thing possible?’

‘Anything’s possible,’ said Nightingale. ‘If your dog was affected along with his master and Coopertown, then it would explain why he was so sensitive to the vestigia.’

I noticed Toby was my dog now. ‘So it’s possible?’

‘Yes,’ said Nightingale, but I could tell he was sceptical.

‘What if the cycle courier is playing Toby’s role and the doctor is taking Coopertown’s?’ I asked. ‘At the very least it wouldn’t hurt to keep an obbo on the doctor until the courier is caught.’

‘Can you handle that?’ asked Nightingale.

‘No problem,’ I said.