‘I vote for the doorway,’ said Reynolds. ‘Unless it goes back to the sewers too.’

‘I doubt it,’ said Kumar. ‘I’m not an architectural prodigy like Peter here but I’m pretty certain this is part of the Underground.’

I looked around. Kumar was right. The room had the cement and concrete squatness that I associated with the mid-twentieth-century sections of the Underground. The late Victorians went for brick and the modern tube stations are all brushed concrete surfaces and durable plastic cladding.

Kumar stepped through the doorway. ‘It’s a stairwell going down,’ he said. ‘But it’s going to be a bugger to navigate without lights.’

‘I’ve got an emergency light,’ I said getting up. I nudged Reynolds with my foot. ‘On your feet, Marine,’ I said.

‘Ha ha,’ said Reynolds, but she dragged herself up.

Kumar stood aside as I stepped into the doorway and, keeping my back to Reynolds, made myself another werelight. It revealed a spiral staircase with wooden banisters and a metal core.

Definitely London Underground, I thought.

‘See,’ said Kumar. ‘It used to go up but it’s blocked off.’

Crudely bricked up with breeze blocks, in fact.

‘Could we break through?’ I asked.

‘Even if we had the tools,’ said Kumar, ‘we don’t know if the top of the shaft is still open. They often just plug them up when an old station site is redeveloped.’

‘Down it is, then,’ I said.

‘How are you doing that?’ asked Reynolds suddenly from behind me.

‘Doing what?’ I said as I started down the steps, increasing my pace.

‘That light,’ said Reynolds. ‘How are you doing the light?’

‘Yes,’ said Kumar. ‘How are you doing that?’

‘It’s just a plasma ball,’ I said. ‘It’s just a toy.’

She turned and walked back into the room. She was, I realised, checking the werelight on the ceiling to see if it looked the same. Why couldn’t I have got a stupid FBI agent? I asked myself. Or, if not stupid, then at least someone stolid and law-abiding – then she wouldn’t even be down here.

I proceeded down the stairs in the hope of forestalling any explanations.

‘I’m not sure I like that fact that we’re going down,’ said Kumar.

‘At least we’re out of the sewers,’ I said.

‘Have you smelt yourself?’ said Kumar. ‘We’re taking the sewers wherever we go.’

‘Look on the bright side,’ I said. ‘Who’s going to complain?’

‘Useful toy,’ said Reynolds. ‘Does it come with batteries?’

‘That reminds me,’ I lied. ‘What made you come underground in the first place?’

‘If I recall correctly,’ said Kumar, looking at her. ‘You owe us an explanation.’

‘His mom showed me his emails before I flew over,’ she said. ‘He talks about being involved in London’s underground art scene – “literally underground” he says in one.’

‘That’s it?’ I asked. ‘For that you climbed into the sewers?’