In the forgotten footage, a phrase came back. ‘I’m my father’ – whatever that meant – was virtually the only information she’d given away. That, and a town near Moscow which wasn’t Murmansk.

She had mentioned a poet. Tyutchev. Dyer looked him up. Feodor Tyutchev. From Muranovo. That was it.

It was a swing in the dark. Dyer called up scientists born in Muranovo. And straight away there he is, Vasily Lavramarov, b. 1941. Looking just like his grandson, like Katya.

Until the moment he saw her father’s face, Dyer refused to believe what he had already guessed. But his doubts evaporated when he read that the atomic physicist Vasily Lavramarov was a member of the 1969 nuclear fusion delegation which had been responsible for building the T-3 tokamak. His old newspaper might have demanded a second source; Dyer needed no further verification. Katya was a child of nuclear fusion. She must have been spying on Marvar since the day she arrived in Oxford, and reporting back to Mr Putin’s chum, Gennady.

Dyer didn’t know how to feel. In his pride, he hadn’t wanted to believe it was all a ruse, her admiration for Leandro, her hurt over Vasily, her attraction to Dyer. The fact that she was sitting seductively in a pub by herself at lunchtime.

She had observed him talking with Marvar, and, after that, wearing Marvar’s coat, and in concert with Gennady had taken the decision that Dyer was a stone that needed to be turned.

Once she had decided that Dyer knew nothing, he was what he said, a washed-up journo desperate to find relevance in a sixteenth-century Portuguese colony in Latin America, then he was history, as unnecessary and pathetic to her as his subject.

Dyer closed his laptop. Yet it didn’t stop the roar in his head. The din was like the tune of that homeless accordionist, the same questions going round and round and round.

If he was to believe Katya, the Russians weren’t holding Marvar. But neither were the Americans, because Updark wouldn’t be looking for him if so. And nor were the Iranians – if indeed it was the Iranians who had tried to grab Dyer. Who, then? The Israelis? The Saudis? The Chinese?

Or was this a wild-goose chase, and Marvar remained at large?

Dyer didn’t want to admit to himself that Marvar might be dead. His essential innocence could not be violated, somehow it would endure. Then he thought of the overcoat upstairs on his bed, like the hide of a hunted mammoth.

But whether Marvar had been captured or killed or was treading the moors around Fusedale was somehow irrelevant. The scrap of paper that he had buried for Dyer to find had made him more alive.