This is the tale of two stories. This is the tale of what Nicolas did next, and what Rachkovsky is about to create in the basement of Rue de Grenelle: a fire balloon that will float out of the nineteenth century with devastating consequences for an entire people. This is not the story of a lost love; yet all stories are stories of loss and love.

Weeks later, at the conclusion of the narration, Vincenzo will push Notovitch for evidence to support his wilder claims.

So much of what Notovitch had told him was, at best, a partial truth. He had embroidered, elided, omitted, exaggerated, fabricated, misremembered and forgotten. He had told a mixture of half-truths and truths-and-a-half. Vincenzo was compelled to do what we all do: piece together a workable version of the world from incompatible stories, knowing that no final truth is available. But inside every ironist is a romantic with a rose between his teeth, struggling melodramatically to get out.

Vincenzo will shake his head almost pleadingly. Something. Anything. He needs some token of authentication, if only to save Notovitch, whom he’s come to like, from the accusation of being a liar.

‘Very well. I must ask you a favour. Would you be so kind as to remove my left slipper?’

Vincenzo hesitates. He’s reluctant to kneel before Notovitch: the act seems charged with an inappropriate deference. He slides a footstool towards the old man’s armchair and seats himself on it. Notovitch raises his left leg. Vincenzo removes the worn carpet slipper and the heartbreakingly darned sock whose odd shape gives a premonition of its abbreviated contents: a foot with only three toes. The fourth and fifth have been tidily removed: a surgeon’s work. But the splash marks on the skin, and the livid gouges, show where the acid had fallen.

‘We had enhanced the Third Section’s reputation at a stroke.’

News of the Geneva escapade had already reached Saint Petersburg, where its success won plaudits and an increased budget for the Third Section. At Nicolas’s debriefing, Rachkovsky presented him with a rose-gold pocket watch to say thank you.

‘The good news is that those two toes entitle you to a significant disability bonus. Good work. And you can get married now,’ he says.

‘There’s something I need to do first. Yulia has something of mine. It’s something I need for my wedding. I’ve been wondering how I can contact her to get it back.’

Fortunately, Rachkovsky’s too buoyed up with his latest triumph to notice that Nicolas has inadvertently composed a riddle to which the answer is: heart.

‘I’ll send her a message. It’ll take a day or two. We use a music teacher to communicate in her area. He travels around giving violin lessons. It’s rather clever because he can go virtually anywhere without arousing suspicion and he’s always carrying a portfolio.’

Wow, thinks Nicolas. Rachkovsky’s either accepted him right into the heart of the operation, or he’s so pleased with himself that he hasn’t noticed that bits of spycraft are practically falling off him.