‘I’ve been looking for you,’ Christophor said.

‘Hello, Inspector,’ Victor said without looking up.

He joined them in watching the smithy at work. Though his knowledge of the craft was not extensive, it did strike him that he was seeing something unusual. It wasn’t horseshoes or blades or ironmongery of a traditional kind that had the large, aproned man bent over his station. Instead it seemed to be more intricate work.

‘Do you often watch a smithy at his business?’ Christophor said.

‘Only when we’re paying him,’ Julia said, his intrusion clearly wearing her patience thin.

‘I see. And what are you paying him to do?’

They exchanged a look. Slowly Victor turned to him. ‘To aid us in an experiment,’ the boy said, expressionless. A chilling child. He would make an excellent magistrate, so I thought.

Christophor considered this, and decided a gamble was appropriate. ‘This wouldn’t happen to be your secret experiment, would it?’

‘I told you not to tell him!’ Julia said.

Victor winced.

Christophor was unduly proud of himself for outmanoeuvring two children.

‘This isn’t the whole experiment, just a single phase,’ Victor said.

The smithy straightened and, bringing a square of metal to his face, blew on his work. ‘There we are, Master Victor,’ the smithy said, showing the boy the still-hot piece. ‘Is that about the right of it?’

Victor moved as close as he dared against the forge’s heat. Christophor followed him. Man and child stared at a six-inch square of scoured metal, engraved into which was what looked like a nest of overlapping circles. In the centre were the letters V and M.

Christophor recognised a witches’ mark, an apotropaic mark, when he saw one – he’d employed many of his own making over the years. A ward against the evil eye. A keep-away that, on occasion, bore talismanic letters of the Virgin Mary.

‘Victor?’ Christophor said. ‘What need do you have for such a thing?’

‘Not here, Inspector,’ the boy whispered.

The smithy looked nonplussed. But his demeanour improved dramatically when the boy handed over a silver kreer.

‘Fine work, Mr Baerson, sir,’ Victor said. ‘When can we expect the others?’

‘Tomorrow noon be appropriate?’

‘The evening would be better.’

‘Right you are, Master Victor. Evening it is.’

Victor offered his hand, which was swiftly engulfed by the smithy’s. Apparently satisfied, the boy passed the square of metal to Julia and then set off down the street at a purposeful pace. He didn’t look back. Julia and my night-brother followed in his wake.

Their destination was obvious, but there was not an insignificant part of Christophor that hoped he was mistaken. Perhaps the mark was somehow related to Victor’s study of the Dreken river? Perhaps the boy feared the influence of dark magics was affecting his experiments there? Perhaps…

But with every corner turned and every street crossed, they drew closer to the start of the track. They passed a bakery, a sweetshop, a wooden toymaker, and each time Christophor felt the faint flutter of hope at the bottom of his throat. Then, as they came to the same spot at the base of the track where he’d stopped that night, he abandoned that hope. He opened his mouth, making to object, but the children continued onwards when he had paused, faltered. He had no choice but to follow.