‘That night, the Mackenzies had gone to a dinner. I’d been up since five o’clock in the morning with Archie . . . I’d put him to bed and he’d kept getting up, wanting to see Gabby, his mother, before she left. He was almost two, and he could reach the door handle to the bedroom to let himself out – she refused to put a child gate up, said they looked untidy. She was angry with him, shouting at me to get him out so she could get ready. She had a temper.’ I pause for a moment, seeing Gabby in my mind’s eye, all dark hair and heaving bosom. She was never maternal, not cut out to be a mother. ‘They left, and finally Archie fell asleep. I was so tired, too tired to even eat dinner, so instead I poured myself a glass of wine, and went out into the garden to have a cigarette. I forgot to pick up the baby monitor.’

For a moment, I am back there, in Killin, standing in the garden of the Mackenzies’ huge stone house. The UK had been in the grip of a short heatwave, the day had been hot, and the evening was still stiflingly warm, rare for this far north. My feet dusty in my worn New Look sandals, the thin cotton of my summer dress brushing against my knees in the warm evening breeze, heavy with the scent of the roses that grow all along the path. I clamp the cigarette between my teeth, the rasp of the lighter and then that first trickle of smoke pouring into my lungs soothing away the stress and exhaustion of the day.

‘I don’t know how long I stood out there for. Long enough to finish my wine and smoke two cigarettes and watch the stars. When I came back in, Archie was at the bottom of the stairs. He’d let himself out of his bedroom and come looking for me. The staircase was polished oak . . . he must have lost his footing and fallen. He was unconscious.’ I feel that familiar, sick, panicky feeling, and I am frightened that if I open my mouth I will vomit all over the table. The crimson stain spreading out across the flagstone floor, the weight of his head as I cradled his tiny skull in my hands, his blood seeping into the skin around my fingernails. I clamp my teeth together, breathing in and out through my nose until I feel under control again.

‘And then what happened?’ DC Bishop’s voice is soft now, her eyebrows creasing together slightly as she listens.