‘See that,’ he pointed at a section of first floor window frame hanging suspended from what looked like a curtain rail. ‘Very shoddy. I’d say our man was not himself when he cast his opening spell.’

He’d been enough of himself to rip out the base of Tyburn’s expensive period staircase, leaving the polished balusters hanging like broken teeth from the handrail. The back wall of the parlour had been smashed into the room behind – the wall mounted TV ripped neatly in half with one part embedded in the ceiling and the other lodged at head height in a kitchen cabinet.

Olivia and Phoebe had been watching Brooklyn Nine-Nine on that TV when the attack started and had only avoided serious injury because they’d both happened to be lying prone on the sofa.

‘Saved by snogging,’ had been Seawoll’s verdict. ‘Let that be a lesson to you.’

Nightingale’s lesson was slightly different.

‘He just went straight in with no thought as to where his targets might be,’ he said. ‘And if you look at the line of his effort there . . .’ Nightingale swept his hand to indicate where a wide crack had shattered the delicate Regency moulding in the corner of the room, ‘you’ll see that it lacks precision. A surefire sign of . . . what, exactly, Mr Grant?’

‘One of the underlying forma was not properly developed,’ I said.

Nightingale’s lips twitched.

‘Can you tell which one?’ he asked.

I studied the crack. I had no idea what the spell would have been, but probably fourth or fifth order given it was doing quite a number of different things at the same time. Since it was shoving masonry around, the spell had to be impello-based but not even I mess impello up. So it probably had to be one of the modifiers.

‘Temperāre,’ I said – totally guessing.

‘Yes,’ said Nightingale. ‘I think you’re right.’

He looked at Martin Chorley’s handiwork and shook his head again.

‘Definitely off his game,’ he said.

Not so off his game that he hadn’t managed to do that much damage in the less than five seconds between his casting the spell and a fountain of water bursting up his trouser leg. I’d have loved to have had CCTV of that, but of course every camera within a hundred metres had gone phut when he cast the spell.

‘Entirely on purpose,’ in Nightingale’s professional opinion.

‘And yet no vestigia,’ I said. At least nothing I could sense. On a Regency street in central London there should have been at least the background afterglow of everyday magic. But standing in front of the ruined house I could feel nothing. Less than nothing, a vast sucking silence. A great absence of ordinary magic.

I’d felt that before.

At the Coopertown house before Punch took a father and annihilated a family.