If Renfrew is put out of temper by Charlie’s change of topic he does not show it. There is no frown, no pursing of the lips. But whatever was boyish in his face dies away, leaves a harder man behind. Not hard, Charlie thinks. Righteous. Rational.

It amounts to the same thing.

“Yes, we travelled far and wide — it was still legal then. The Continent. All the colonies. And beyond. Beyond the pale of civilisation.”

“I think I know what you were looking for. The birthplace of Smoke. Where it came from originally. The source.”

Renfrew shakes his head. “An intelligent surmise, Mr. Cooper, but wrong. It’s what I thought when Baron Naylor first explained his theories to me, and asked me to travel with him. It was the summer after my first year at Cambridge. I was only a little older than yourself. The baron had invited me to stay with him in the splendour of his manor. We read, went out riding, hunting, boxed. Oh, he picked me well! A scholarship student. Poor; risen above my station. In thrall to his title as much as his intellect.”

There is something scornful to the way he says it, something rigid about Renfrew’s posture. It takes Charlie a moment to understand it. Here he is, the scholarship student, instructing the English elites at the finest school in the country. No, not instructing. Sitting in judgement. He is not in thrall to titles anymore.

“Our first journey was to Bulgaria. Gathering evidence, in old monastery libraries. But by the next summer the baron had a new idea. Something rather more daring. If Smoke only came to Europe in the seventeenth century, he reasoned, there might be places in the world it had not yet reached. Remote places, at the very edge of things. You see, he was looking for an innocent.”

Charlie remembers the picture. A girl chained to a wall: twisting her head, away from the camera. A girl that grew up to save Thomas’s life.

“You found one.”

“We found a whole people. Or at least we heard about them. A people without Smoke. Living in tiny tribes in a land of eternal ice. Hunting whales from boats no bigger than a dinghy. Eating raw seal. The tribes to the south thought of them as demons. When they saw them, they turned and ran away.

“We had a problem then. It wasn’t just that none of our guides would take us to them. There was also the question whether contact with us would infect the tribe. Imagine destroying the very specimen we had travelled so far to collect! We spent weeks debating the problem.