Once the victim had been spotted on the platform it took the station manager less than three minutes to reach him but he was definitely, as the station manager put it, brown bread by the time he found him. We didn’t know how he’d got in the tunnel and we didn’t know how his killer had got out but at least, once forensics had processed the wallet, we knew who he was.

‘Oh bollocks,’ said Seawoll. ‘He’s an American.’ He passed me an evidence bag with a laminated card in it. At the top was NEW YORK STATE, below that DRIVER LICENSE, then a name, address and date of birth. His name was James Gallagher, from some town called Albany, NY, and he was twenty-three years old.

We had a quick argument about what time exactly it was in New York before Seawoll dispatched one of the family liaison officers to contact the Albany Police Department. Albany being the capital of New York State, which I didn’t know until Stephanopoulos told me.

‘The scope of your ignorance, Peter,’ said Seawoll, ‘is truly frightening.’

‘Well our victim had a thirst for knowledge,’ said Stephanopoulos. ‘He was a student at St Martin’s College.’

There’d been an NUS card in the wallet and a couple of business cards with James Gallagher’s name on them and what we hoped was his London address – a mews just off the Portobello Road.

‘I do like it when they make it easy for us,’ said Seawoll.

‘What do you reckon,’ said Stephanopoulos. ‘Home, family, friends – first?’

I’d mostly kept my mouth shut until then and I’d have, frankly, preferred to have sloped off and gone home but I couldn’t ignore the fact that James Gallagher had been done in with a magical weapon. Well, magical pot shard anyway.

‘I’d like to have a look round his gaff,’ I said. ‘Just in case he was a practitioner.’

‘Practitioner eh?’ asked Seawoll. ‘Is that what you call them?’

I went back to keeping my mouth shut and Seawoll gave me an approving look.

‘All right,’ said Seawoll. ‘Home first, round up any friends and family, get him time-lined. BTP are going get some bodies down here to sweep the tunnels.’

‘Transport for London aren’t going to like that,’ said Stephanopoulos.

‘That’s unfortunate for them, isn’t it?’

‘We should tell forensics that the murder weapon may be archaeological,’ I said.

‘Archaeological?’ asked Seawoll.

‘Could be,’ I said.

‘Is that you’re professional opinion?’

‘Yes.’

‘Which as usual,’ said Seawoll, ‘is as about as useful as a chocolate teapot.’

‘Would you like me to call my boss in?’ I asked.