‘Do you think I’m making this up?’ asked Mrs Coopertown. She had the startled-rabbit look that civilians get after five minutes of helping the police with their inquiries. If they stay calm for too long it’s a sign that they’re professional villains or foreign or just plain stupid. All of which can get you locked up if you’re not careful. If you find yourself talking to the police, my advice is to stay calm but look guilty; it’s your safest bet.

‘Not at all,’ said Nightingale. ‘But since he’s the principal victim we’ll need to take his statement.’

‘He’s in Los Angeles,’ she said. ‘He’s coming home late tonight.’

Nightingale left his card and promised Mrs Coopertown that he, and by extension all right-thinking policemen, took attacks by small yappy dogs very seriously and that they would be in touch.

‘What did you sense in there?’ asked Nightingale as we walked back to the Jag.

‘As in vestigium?’

‘Vestigium is the singular, vestigia is the plural,’ said Nightingale. ‘Did you sense vestigia?’

‘To be honest,’ I said, ‘nothing. Not even a vestige.’

‘A wailing child, a desperate mother and an absent father. Not to mention a house of that antiquity,’ said Nightingale. ‘There should have been something.’

‘She seemed a bit of a neat freak to me,’ I said. ‘Perhaps she hoovered up all the magic?’

‘Something certainly did,’ said Nightingale. ‘We’ll talk to the husband tomorrow. Let’s get back to Covent Garden and see if we can’t pick up the trail there.’

‘It’s been three days,’ I said. ‘Won’t the vestigia have worn off?’

‘Stone retains vestigia very well. That’s why old buildings have such character,’ said Nightingale. ‘That said, what with the foot traffic and the area’s supernatural components, they certainly won’t be easy to trace.’

We reached the Jag. ‘Can animals sense vestigia?’

‘It depends on the animal,’ said Nightingale.

‘What if it was one that we think might already be connected to the case?’ I asked.

‘Why are we drinking in your room?’ asked Lesley.

‘Because they won’t let me take the dog into the pub,’ I said.

Lesley, who was perched on my bed, reached down and scratched Toby behind the ears. The dog whimpered with pleasure and tried to bury its head in Lesley’s knee. ‘You should have told them it was a ghost-hunting dog,’ she said.

‘We’re not hunting for ghosts,’ I said. ‘We’re looking for traces of supernatural energy.’

‘Did he really say he was a wizard?’

I was really beginning to regret telling Lesley everything. ‘Yes,’ I said. ‘I saw him do a spell and everything.’

We were drinking bottles of Grolsch from a crate that Lesley had liberated from the station’s Christmas party and stashed behind a loose section of plasterboard in the kitchenette.

‘You remember that guy we arrested for assault last week?’