Foma still ran the risk, however, that he might meet a patrol which did have a Russian speaker in its ranks, and then he would be found out. Whether through this reasoning, or out of instinct, his approach to avoiding the problem was to avoid being seen. As a patrol (or indeed anyone) came near he would step into some dim doorway or alley and wait for them to pass. His skill at hiding in darkness was remarkable. At one point, when I was watching him from the far end of the street, he heard approaching footsteps and flung himself into the shadow of the wall at the end of a block of houses. It was as if he had vanished before my eyes.

I watched for several minutes as first an organized patrol and then a rowdy group of off-duty soldiers came past, and still he remained invisible. I got out my spyglass and looked again at the place where I had last seen him, but I could make out nothing but the vague shapes of dark shadows cast against the wall. Then, suddenly, what I was looking at transformed; not through any intrinsic change in itself, but simply by my unconscious reappraisal of what I was seeing. I wasn't staring at a shadow, but at the side of Foma's face, pressed against the wall in utter and complete stillness. It was that ability to stay quite still that somehow allowed him to disappear. His dark coat hid most of his body. Looking around further, I could also make out his hand, pressed against the wall as if reaching out to those who were passing by, but again implausibly still. Of the arm that I knew must lie somewhere between his hand and his face, I could make out nothing.

Looking back to his face, I noticed that there was one minuscule hint of movement. His eyes were flicking back and forth. They say that when a man dreams his body remains quite still and yet his eyes continue to move, indicating physically to the real world in which direction the dreamer is looking in his mind. The only difference was that Foma's eyes were open, following the stragglers of the off-duty soldiers as they tottered past.

After the last trailing man had gone by, his footsteps fading into the night, Foma moved and was suddenly quite visible once again. But he didn't continue on his way. He liked what he had seen and began to follow the soldiers back up the road. This time it was my turn to step back into the shadows as he passed.

Foma followed the soldiers, I followed Foma and we all headed gradually eastward into the outskirts of Kitay Gorod. Fresh flames shone to the south-east, but the area in which we found ourselves remained untouched, not just by fire, but by the French. Beyond the small troop that we were following, we saw no other patrols. Soon the soldiers came to their destination – an abandoned school building that they were using as their barracks. With the same laughter and jokes that had accompanied their entire journey across town, they made their way into the building and closed the door.

Foma was only a short way behind them, but again he had stood stock-still, with his back pressed to the wall, and had remained unseen by anyone but me. Hiding myself at the end of the street, I watched Foma to see what he would do next. Now that the boisterous revelry of the soldiers had ceased, my own breathing sounded deafeningly loud. Foma passed back and forth outside the school, gazing up at the high windows, reminding me of a cat pacing up and down beneath a caged bird, never doubting its ability to climb up and take the puny, twittering creature, but simply looking for the best route to ascend – the best route being that by which the cat is least likely to be found out.

After a little consideration, Foma stopped beneath one of the windows, deciding that it was the easiest one to reach, or perhaps noticing some slight clue that suggested he would be able to break it open. Without hesitation, he began to climb the wall. It was an astonishing feat, one which I could not have achieved, and neither could any but the most expert of climbers. He found every tiny crevice and fissure in the wall and somehow managed to insinuate his fingers or toes deeply enough inside to gain some purchase. Just as when he had been hiding, his body clung inseparably close to the wall, and as he moved each limb in turn, sliding it across to its next grip, his body flowed like water across a rock, never venturing away from the precipice he scaled in case it unbalanced him. The impression was of some sort of lizard or insect – no, neither of those, instead a spider – climbing up that wall, but I realized that Foma's achievement was not in truth inhuman, but superhuman. Any man with the strength and skill and experience – and, it has to be said, daring – could have achieved it. I was not such a man, and it was difficult to conceive that a man so unprepossessing as Foma could in any area of activity be so exceptionally talented.

He reached the window and opened it without trouble, scuttling into the building with a swiftness that almost made it appear he had been pulled from inside. There was no way that I would be able to follow him, nor had I any desire to find myself trapped in a room with him as he discovered that I had been following him.

I crept up to the school building and listened. All was silent within; no hint of what Foma might be doing inside, nor any reaction from any of the soldiers who slept there. There was little I could do but wait, and hope that Foma would leave by the same window he had entered, or at least from the same side of the building. The house opposite had a rather grand portico and so there I sat, leaning my back against the wall and hidden from the school by one of the pillars.

I suspect I may have dozed off, but it felt like only seconds later that I was being challenged, in heavily accented Russian, by the commanding officer of a small squad of French troops.

'What are you doing here?' he barked.

'Sleeping, sir!' I leapt to my feet in an effort to show respect, but I realized that if I wasn't careful, I might betray my military background.

'Don't you have a home?' As the lieutenant spoke, I noticed behind him the window of the school across the street swing open once again.

'It's been occupied, sir,' I replied, trying not to look at the window and thereby betray Foma, 'by your compatriots.'

'And where was that?'

This was a tricky question. I tried to recall somewhere close by where I had seen French soldiers billeted.

'Kolpachny Lane, sir.' Behind him, the figure of Foma slipped to the ground, not quite jumping, not quite climbing; flowing – slower than water but faster than honey – like blood. He passed across the wall as the shadow of a stationary object cast by a moving light.

'I see,' continued the officer. It looked like he believed me and had some sympathy for my predicament. 'But I can't help that. The men have to sleep somewhere.'

I nodded. Foma walked silently away down the street, almost swaggering compared to his earlier furtive gait, as if proud of what he had achieved within the temporary barracks. Whether he glanced over towards me and the French soldier, I don't know. Even if he had, he may not have recognized me. He certainly made no action to come to my assistance.

'I have to sleep somewhere too,' I told the lieutenant, trying not to appear so submissive that I might arouse suspicion.

'That's as may be, but you can't sleep here. That's a barracks over there.' He glanced over his shoulder, but Foma had already vanished into the night. 'We can't have the natives loitering around here.'

'I'm sorry, sir,' I said. Anger began to well up inside me as he spoke, particularly at dismissive words such as 'native', but it was not the anger of Captain Aleksei Ivanovich Danilov – he understood that this was just the bluster of a frightened junior officer in a foreign country. It was the anger of the homeless Russian butler that I had become, much as I always became whoever I had to pretend to be. It would not convince this lieutenant if the Muscovite before him simply stayed calm. I had to stay calm, but to do so in spite of myself, and make it clear to him that I was angry and urgently containing myself so as not to show it. So many layers of deception are too difficult to juggle. It is better simply to believe it oneself, then one cannot be doubted by any man.