Ayto led Crimm through a smaller, windowless parlour that ran off from the back of the room they’d been in, took an oil lamp from the wall, and then went on through another dusty door, down a darkened passageway, and into another sitting room, or office. There was a desk piled with curling paper, a smell of must and dust, and an unlit hearth like a gaping black mouth.

‘I did some exploring back here earlier, before you showed up with Aranx.’

‘It’s not too cold in here,’ Crimm observed.

‘We’re already inside the Wall. Old Thaxa’s property goes on further into the growstone. I don’t think anybody knows how deep these old chambers go, or how much Thaxa actually owns. But according to Moerx, the servant, there should be another door at the back here . . .’

The rear wall was covered by a tapestry bearing stylised Northland icons, concentric circles with stabbing radial lines. Ayto pulled the tapestry down to expose a heavy wooden door. This wasn’t locked, but was stuck in its frame, perhaps the wood had swollen, and it took the two of them to shift it.

Then another corridor. And another room and corridor, and another.

And they emerged into a much larger space. Ayto lifted the lamp high. The walls were just rough growstone, the floor bare and roughly laid, the roof so high it was almost out of sight, but Crimm saw that it was well constructed, of vaulted domes of growstone. He thought he saw a glimpse of daylight from the roof. He pointed. ‘An air vent?’

‘I think so. Moerx said there was a hearth – look, over there.’

Crimm walked a bit further, away from the circle of light cast by the lantern. The hearth looked very crude, just a heap of bricks in the corner, set up under the vent. There were shadowy heaps in the corners and by the walls: bits of canvas maybe, wooden pallets. And Crimm made out stains on the walls, greenish-grey, that ended in a band some distance above his head.

‘Must be an old warehouse,’ said Ayto. ‘Something like that.’

‘No, I don’t think so. Look at those stains. It looks as if water was kept here. It’s some kind of huge cistern. Or was. Maybe the system it was part of was abandoned. And then it’s been reused, by somebody camping here – whoever built that hearth.’

‘That might have been a long time ago. And then it was forgotten, and the Wall has sort of grown out around it. Moerx told me about it because I asked him how deep the house went into the wall. Just being nosy. He’s looked around before – well, you would, wouldn’t you? When he described this place it gave me an idea.’

‘Hmm. I don’t always like your ideas, Ayto.’

‘We could use this place.’

‘There’s certainly some firewood we could use—’