The doctor took a biscuit from the plate she held out, and said, ‘Elsie.’

‘He was, Douglas. You’ve said yourself.’

‘Aye, well.’ The doctor settled back into his chair and set his biscuit neatly on the saucer of his teacup. The curtains at the end wall of the sitting room were drawn well back this afternoon to let in the sunlight, which fell with a comforting warmth on my shoulders as I chose a biscuit myself, from my seat by the long row of glass-fronted bookcases.

‘Daniel Defoe,’ Dr Weir said, ‘was doing what he thought was right. That’s what motivates most spies.’

Elsie took her seat beside me, unconvinced. ‘He was doing what he thought would save his skin, and line his pockets.’

The doctor’s eyes twinkled briefly, as though his wife’s stubborn dislike of Defoe struck him as something amusing. To me, he said, ‘She won’t even read his books.’

‘No, I won’t,’ Elsie said, firm.

‘Even though the man’s been dead too long,’ her husband pointed out, ‘to profit from the royalties.’ He smiled. ‘Defoe,’ he told me, ‘was a stout supporter of King William, and no friend of the Jacobites. But he made the mistake, near the start of Queen Anne’s reign, of publishing a satirical pamphlet that the queen didn’t care for, and so he was arrested. He was bankrupt as well, at the time, so when the government Minister Robert Harley offered him an alternative to prison and the pillory, he leaped at it. And Harley was, of course, the queen’s chief spymaster.’

I knew the name, from my own reading.

‘Harley,’ Dr Weir went on, ‘was quick to see the benefits of having someone like Defoe to write his propaganda. And being a writer, Defoe was well-placed to do more for the government. Just before the Union, Harley sent him up to Edinburgh, to work in secret for the Union cause and to discredit those opposed to it. Defoe, as his cover, let dab he was writing a book on the Union and needed some help with his research. Not unlike what you yourself are doing, here in Cruden Bay.’

And, like myself, Defoe had found that people, by and large, were happy to sit down and tell a writer what they knew.

‘They didn’t think he was a spy,’ said Dr Weir. ‘But everything they told him found its way to Harley, down in London. And Defoe was good at learning things, observing, and manipulating. There’s no doubt that he had an impact on the Union being passed.’

‘A weasel,’ Elsie said again, and set her teacup down with force.

I asked, ‘Would he have ever been to Slains?’

‘Defoe?’ The doctor frowned. ‘I wouldn’t think so, no. He might have known what they were up to, and he doubtless would have met the Earl of Erroll, who was often down in Edinburgh, but I’ve not heard Defoe came up to Slains. But there were other spies. And not only in Scotland,’ he told me. ‘The English took a great interest in what went on at Saint-Germain. They had a whole network of spies based in Paris, and some at Versailles, with their ears to the ground. And they even sent people right into Saint-Germain, when they could manage it. Young women, usually, who slept with men at court and carried back what news they could.’

‘The tried and trusted method,’ Elsie said, to me, her mood improving now that we’d got off the subject of Daniel Defoe.

Dr Weir was thinking. ‘As for Slains…I’ll have to do a bit of reading, see if I can’t find a spy or two who might have ventured that far north.’

And with that settled, we moved on to talk of other things.

I stayed much longer than I’d meant to. By the time I left them it was dusk. The rooks were gathering again above the Castle Wood, great clouds of black birds wheeling round against the night-blue sky and cawing raucously. I quickened my steps. Up ahead I could see the warm lights of the Kilmarnock Arms spilling out through its windows and onto the sidewalk, and crossing the road I turned briskly down Main Street, my eyes on the dim looming shapes of the dunes rising up on the opposite side of the swift-rushing stream.

It was windy tonight. I could hear, farther off, the great roar of the waves as they rolled in to break on the beach and slip backward, collecting their strength to reshape and roll shoreward again in an endlessly punishing rhythm.

It had a hypnotic effect. When I started to climb the dark path up Ward Hill, my steps were all but automatic and my mind was filled with waking dreams. Not all of them were pleasant. There was something unseen on that path, not chasing me but waiting for me, and as I tried hard to fight the rising sense of panic gripping me, I suddenly stepped forward into nothingness.

It was like stepping off a curb without expecting to. The ground was there, but lower than I’d thought that it would be, and when my foot came down it came down hard into a deep rut underneath the thickly tufted grass, and twisted so I lost my balance and began to slide.

There was no time to think. Pure instinct made me grab at anything to stop myself, and by the time I’d registered the fact that I had left the path and was now slipping dangerously down the steep side of the hill above the sea, my fall was stopped abruptly by a line of leaning temporary fencing that was strong enough at least to hold me while I tried to catch my breath.

From my ankle came a fiercely shooting pain that burned like fire. In full awareness now, I looked up at the spot from which I’d fallen. What a stupid thing to do, I thought. The path would have been plain to see, despite the growing darkness. I had no excuse. Except…