This afternoon she’d been more a young woman, already now entering into her late teens with all the mature poise that girls of that long-ago time had most probably needed to gain, unlike girls of my own generation. My own teenage years had been freer, but from the way Anna had set her slim shoulders I’d guessed she had already learnt how to balance the weight of responsible burdens.

But still, she’d seemed loved, and her clothes, if not fancy, had looked to be well made and fine. She’d been wearing a long cloak and hood when we’d first seen her, walking in the snow of the great space beside the Admiralty.

The hood, falling forward, had covered her hair and a part of her face, so it hadn’t been till she had entered the house and had hung up her cloak in the lobby that I had been able to see what she actually looked like.

She wasn’t a stunningly beautiful girl, but her features were even, and lively enough to be pretty. Her eyes were still lovely, that softly grey-green colour, under arched eyebrows that matched the dark brown of her lashes. Her hair had stayed dark brown as well, and it still fell in curls round her forehead and cheeks.

She stood close to my height, neither tiny nor tall, with a slim build that gave her a natural, tomboyish grace, and she seemed – as she had when a child – to be always in motion, if not in her body, then in her intelligent mind which revealed itself plainly whenever one looked at her eyes.

Rob was following my train of thought. ‘Does she look as she did when you saw her the first time?’ he asked.

‘I’m not sure. Maybe.’ I’d only had a brief glimpse of her then, and I couldn’t be certain.

Rob shrugged. ‘We’ll ken more,’ he said, ‘after tonight.’

It was already nine in the evening. The sun had just set and the light from inside the warm restaurant reflected back now in the darkening windows. ‘Tonight?’

‘Aye, it’s early yet. We’ve only got … what? Three days?’

‘Nearly four.’

‘You’ll be working for some of that,’ Rob pointed out. He had finished my pie and was draining the last of his lager, his eyes shining more brightly blue than they ought to have done. Two strong lagers, I thought, drunk as quickly as he had downed those ones, would have an effect.

I tried the tactful approach. ‘Are you sure that you’re up to it?’

Rob grinned. ‘You mean, am I blootered?’

‘Your accent is thicker.’

‘I’ve no got an accent.’ His arch look accused me of being delusional. ‘But if you have doubts, maybe you should do some of the driving.’

I said, ‘We’re on foot.’

‘So we are.’

‘So that doesn’t make sense.’

Unconcerned, he stood smoothly and shrugged on his coat before gallantly helping me into mine. ‘Where,’ he asked, ‘was the Tsar’s palace? The one Gordon sent Anna to?’

I remembered the snow, and the sledges; the bite of the wind. ‘That would have been the Winter Palace. It’s not far.’

It was, in point of fact, a short walk away in the gathering darkness. We crossed one canal by its bridge and strolled down on its opposite side, with the lights from the buildings all round making shimmering points of bright colour that danced in the black water.

Rob took my hand in his own, and I didn’t object. I suspected he’d done it without really thinking, his full senses occupied elsewhere, but I liked the feel and the warmth of it; and when we turned onto the darker canal that led up to the Neva, I was grateful for that contact to assure me I was safe, because at this hour of the evening, even with the few old-fashioned lamps spaced out along the buildings, this was not the kind of place where I’d have come to walk alone.

Our footsteps fell with echoes on the tilting granite paving stones, and echoed still more wildly from the high walls of the buildings to each side of the canal that made the passage feel like some deserted alley streaked with strange distorted shadows. At the farther end, beyond the small arched bridge that marked the edge of the Embankment, cars chased back and forth along the street that ran along the river, in a constant swishing pulse of tyres that faded to the distance, but that noise was muted here beneath the constant slap of water on the cold and slippery walls of the canal itself, its restless surface several feet below the weathered iron railings running at my side.

This was the Winter Canal, spanned up ahead by two bridges – the small one at ground level, and above that the old gallery that ran high over it, a graceful curve built to connect the upper storeys of the Hermitage Theatre on our side of the canal and the even older building on the other, all enclosed with rows of windows that looked lovely in the daylight but at night gave me the feeling I was being watched.

‘The Winter Palace used to stand right there,’ I said, and pointed up ahead to the pale walls we were approaching. ‘There are drawings of it in my grandfather’s book … well, drawings of all the Winter Palaces built on this site, actually. The second one, the one Peter the Great died in, was just sort of absorbed into the next, then eventually all that was torn down to put up this theatre.’ I gave him a short history of how the theatre had come into being in the late eighteenth century, and how it had fallen into disuse in the Stalinist years, and how it had recently been lovingly restored. ‘And while they were restoring it, they found bits of Peter the Great’s Winter Palace preserved underneath where the stage is, and all along here. There was part of the original courtyard, and several rooms, and all that’s been restored as well, inside,’ I said. ‘And here, just here, is a bit of the palace’s old façade. See how this section of wall is a different design?’