Because it was all hugs and feasts and exclamations of joy for James, and never mind the number of times Zach had personally saved Stephen’s arse or fixed some above-ground problem, because Zach wasn’t a descendant of the Beales or Gallaghers. No fatted calf for Zach – not that they actually ran to a fatted calf. ‘But still,’ said Zach. ‘A bit of appreciation would have been nice.’ Which concluded a textbook illustration of why you should say as little as possible when being interviewed by the police – up until he gave us a motive, his resentment, me and Lesley had pretty much written him off as a suspect.

Now me and Lesley exchanged looks – I could tell she didn’t really think Zach did it, either. It wasn’t until I looked away that I realised that I’d read her expression off her bare face without reacting to what her face had become.

‘Does Graham Beale get the fatted calf?’ I asked. ‘What about Ryan Carroll?’

‘Who’s Ryan Carroll?’ asked Zach

‘Famous artist,’ I said. ‘James was a fan.’

‘Don’t know him – sorry,’ he said. ‘Can’t know everyone. But if he was the right Carroll they’d have let him in too.’

‘What about Graham Beale?’ I asked. ‘The managing director.’

‘He used to visit,’ said Zach. ‘But it was his brother who spent time down there. Mad for digging he was – sad really, him dying like that. Stephen says they never saw Graham Beale again.’

‘How many of them are there?’ asked Lesley.

‘Don’t know,’ said Zach.

‘Ten, twenty, two hundred?’

‘More than twenty,’ said Zach. ‘Several families at least.’

‘Families,’ said Lesley. ‘Jesus.’

‘They’ve been minding their own business for hundreds of years,’ said Zach. ‘I bet your Master didn’t even know they were there. And what now? You going to go down there mob-handed? When you find out their kids haven’t gone to school you going to call in social services, do them for truancy, living under ground without a licence?’

He glared at me.

‘You don’t know what you’re going to do – do you?’

He was right, I didn’t know what I was going to do, but then that’s what god created senior officers for.

Not that they knew what to do either.

‘Did you know about these people?’ Seawoll asked Nightingale.

We’d convened in front of the murder inquiry whiteboard, which was covered in timelines, notes and pictures of people who had had just become totally irrelevant.

‘No,’ said Nightingale.