I reckoned that by the time the sentry came round again – if he made it at all – our scent would have left the frosty surface. With the ground so soundly frozen, our boots hadn’t left any traces on the fence itself.

We slipped out from our heap of pine-tops, back into the standing trees, and crept left-handed round the outcrops of rock, following the contour, the hill falling to our right. According to the map, which I’d tried to imprint on my brain from the satellite data, the villa would be below us.

From his station a pace behind me Sasha put a hand on my arm. I stopped to listen. He was pointing down-hill. When I turned my head in that direction I heard what he’d detected: a faint hum, something like an air-conditioning unit. We moved on a few yards, looked over a rocky ridge, and saw the house rising tall from a levelled-out plateau below.

‘Hell of a place,’ I whispered.

From Anna’s photographs I recognised the steep roof and high walls, glowing pale in the moonlight, but the whole place looked more formidable than I’d reckoned. There were three main floors above ground level, a fourth with dormer-windows sticking out of the roof, and some kind of a basement. At the front, on our right, five cars were parked, and on the side facing us a ramp led down to a sunken garage.

‘Jesus!’ I whispered. ‘It’s just like the cellar at the Embassy.’

‘The Embassy?’ I heard Sasha turn his head to look at me.

Suddenly I realised what I was saying. ‘You know – in the courtyard . . .’ Christ! ‘Oh no. Sorry. I was thinking you’d been with us. We stored some kit at the back of the British Embassy in Moscow. There was a garage entrance a bit like this.’

Thank God, he didn’t show the least curiosity.

‘Beeg house,’ was all he said. ‘Where are your men?’

He meant that it might be one hell of a job to locate them – and he was right. For the moment I concentrated on the layout of the place.

Akula had good comms, obviously: we could see a couple of dish aerials bolted on to the wall beneath the eaves. There were video cameras mounted on the corners of the building, and what looked like an infra-red device covering the driveway. But half an hour’s observation convinced me that there was no patrol immediately round the house: Akula was relying on the fence to keep intruders at a distance.

From where we lay we could see the approach road snaking off down the mountainside to our right, and once I was confident that nobody was moving inside the compound, I decided to recce the track, right down to the barrack huts, or whatever they were, at the bottom entrance.