For a moment, I was puzzled. Then I saw that we had been about to pass an open gate with a faded stone lion standing guard and a wooden sign marked Moxham Hall. We must have arrived at the outskirts of the village. This was the house where Trevor and Annabel Longhurst had been living – at least occasionally – when their ten-year-old son had managed to kill his deputy head.

The driver had reacted too slowly and shot a few metres past the entrance. He muttered to himself as he reversed the car and then turned into a ribbon of neatly laid gravel that led us through the thick woodland purposely designed to hide the house from the road. After about a minute, we emerged into an estate that could have been described as a kingdom in itself. Moxham Hall was a sprawling, nineteenth-century manor surrounded by perfectly striped lawns reaching as far as a low metal railing. Miles of grassland stretched out on the other side, different shades of green rising and falling over hills and continuing as far as the eye could see. As we swung round an improbable white marble fountain – Neptune holding a trident, fighting off an army of cupids and dolphins – my eyes took in rose gardens, ornamental gardens, vegetable gardens and rockeries. And there was the famous helicopter pad, a white H stamped into a circle of mauve asphalt. My first impression was that the house was beautiful, with its patterned brick and limestone façade, the rows of symmetrical windows, the grey tiles and chimneys. But as we drew closer, I noticed the modern additions: the out-of-scale conservatory, the fake portico around the front door, the glass and steel shell surrounding the swimming pool. There was something a little soulless about Moxham Hall. I could imagine it being rented out as a posh wedding venue. It wasn’t somewhere I would want to live.

The taxi stopped. We got out.

‘What are you hoping to find here, Hawthorne?’ I asked.

‘Nothing much, mate. But this is where Harriet’s book opens. And since we were passing, I thought we might as well have a look.’

‘I don’t think anyone’s around.’

And yet someone had to be working here. It was obvious from the lawns and the flower beds, the exaggerated neatness of everything. The house was being looked after – and with all this land, so many rooms, it was going to take more than one visit a week. Feeling very much like a trespasser, I followed Hawthorne to the front entrance and watched him press the doorbell. It made no sound, or at least none that we could hear from outside. We waited. Nobody came.

‘What now?’ I asked, thinking we ought to move on to the village.

I was answered by the sound of footsteps on the gravel and a man appeared from around the side of the house, a groundsman or a gardener by the look of him. He was wearing a jacket, waistcoat, yellow cravat and expensive wellington boots. All that was missing was the shotgun under his arm and the Labrador Retriever. As he drew closer, I saw that he was in his sixties, perhaps even older, beaten about by the seasons. The sun had left a red welt on the bridge of his nose. The cold had scarred his neck with ugly patches of psoriasis. The rain had drawn the colour out of his cheeks and the wind had thrown his hair into permanent disarray. Just looking at his face, I took in a whole year of Wiltshire weather.