‘Well, they’re rare, hard to spot, even harder to track, and clever, too. You set a trap, they’ll use a stick to spring it, and eat the bait. But old Mercy caught two alive and sold them to me, and I sent them off to Master Able. Helped him prove that they were not related to something similar that died out at the Burn Line, but had developed from rats in some kind of parallel fashion.’

‘Master Able called it functional selection,’ Pilgrim said. ‘Two species that live in the same way can come to look somewhat alike, and possess similar features and habits, even though they are descended from different stock.’

‘I suppose you must have picked up a fair bit of his schooling.’

‘Not nearly enough,’ Pilgrim said.

The road narrowed and grew ever more rutted, winding up a steep slope in long, lazy curves. The trees thinned and the trotcart turned onto a track that followed the crest of a bare ridge, meandering past outcrops of rock and runouts of loose stones, stands of ferns and clumps of gnarled junipers. A range of mountains lay off to the west, peaks lost in cloud. At last, Righteous pointed to a thread of smoke rising beyond a distant patch of trees, told Pilgrim that was where Mercy had pitched his camp.

It was little more than a slant of canvas in a space pinched between rugged boulders. Mercy Redvine was waiting for them by the campfire. A spry weatherbeaten person with a grey muzzle and tattered ears, barefoot and bare-chested in canvas trews held up by a rope belt knotted under the swag of his belly, he gave Pilgrim a searching look as Righteous introduced him.

‘Righteous told me your boss died. Said you were carrying on his work.’

‘I’m going to try my best.’

‘I see you walk with a cane and haven’t changed out of your city clothes, but it’s no matter. The place where I saw the ghost lights is just along the ridge, and we can ride most of the way in Righteous’s trotcart.’

‘I’d like to hear the story of your encounter,’ Pilgrim said. ‘If you don’t mind telling it again.’

‘To judge if I told it straight the first time?’

‘Talking it through may help you to recall fresh details,’ Pilgrim said.

No point explaining that the real reason was to get around any claim Master Able’s kin might make on the original interview.

‘I know it sounds far-fetched,’ Mercy said. ‘But I also know that what I saw was as real as the three of us standing here. If you want to hear it, let’s make ourselves comfortable. I don’t have much, but I’m happy to share it.’