After agonising over the parting gift, Vincenzo settled on a book from a dealer on Charing Cross Road: a copy of The Divine Comedy in Italian. Notovitch seems genuinely surprised and moved. He whistles at the porter and gestures for him to return. He unclasps the trunk and opens the lid. From inside, he removes an object which he presses into Vincenzo’s hands. Skobelev’s flask.

Too much? I think so. It feels a little Hollywood. Perhaps it’s MacGahan’s chapan instead, tied into a bundle with knotted string and naphthalene-impregnated paper.

That doesn’t seem right either.

How about this: perhaps he takes out a billfold, removes two five-pound notes and hands them to Vincenzo?

No, that’s completely wrong – that last gesture only demeans both men.

Perhaps the precise detail is unimportant.

Do they embrace? Definitely not. They shake hands with a certain guarded respect, knowing there is no basis for friendship and little chance of meeting again.

The guard blows his whistle. Notovitch gets aboard. The train departs.

4: CONVOY SIXTY-EIGHT

LOOK: A COLOURED MARBLE TURNING IN A SEA OF INK. As it rotates, slowly, anticlockwise, the dark line of approaching sunset gobbles a continent puckered with mountains and vast belts of olive forest. Distant wind shirrs the blue enamel of its oceans. It is an earth. Not exactly the earth, but a planet very much like ours.

You recognise this church. In our world, it’s called the Saviour on Blood. Here it has other names: khram Khristusa neschetnykh del, the Church of Christ of Myriad Things, or, more formally, the Church of the Pleroma.

Inside, the walls are covered with mosaics that tell a story you’re familiar with: a shaven-headed man drinks water from a cleft rock; here, he sits in contemplation among orange-robed adepts.

Here’s one of Notovitch himself. It shows our hero in the library at Hemis, examining the volumes of the secret books. Its intent is narrative rather than devotional – in other words, you’re not supposed to pray to it. And yet the depiction of the lama pushes the orange of his robes as close to radiance as Church doctrine will permit. The artist seems to have been influenced by images of Joseph Smith encountering the Angel of Moroni: there’s the same surprise on the young man’s face, the same transfiguring light surrounding both figures. It’s probably just a coincidence. I expect all annunciations are vaguely alike.

This is one world where the fates of Rachkovsky’s and Nicolas’s books have been reversed: where the Protocols sank like a stone and The Unknown Life swept across the world and acquired believers. It is a world where a set of poisonous certainties has been exchanged for the inclusive story that Nicolas found. This dream seems close to what Notovitch hoped for. But the fantasy is so remote that the dream threatens to grow thin and colourless before our eyes. The world where this happened is quite another story.