Now we’re going back in earnest, past the grey decades of stagnation, Stalin’s death, the terrible siege of World War II, the purges, the heady revolutionary years, through times when the deconsecrated church is a warehouse and a morgue. The buttress on which it stands draws back from the canal. The building vanishes. The church is gone. We’re standing on bare pavement. It’s March. The air is damp and raw, just above freezing and the worse for it.

We should probably move to the other side of the canal. Here, in Russia, in 1881, there’s a desperate edge to the search for better stories.

Pulled by a pair of horses and flanked by half a dozen Cossack outriders, the Tsar’s carriage is approaching. It’s somehow smaller than you would expect – smaller, anyway, than the armoured limousine with tinted windows a head of state would ride in now. His Imperial Highness, Tsar of all the Russias, has just come back from the trooping of two battalions of guards. A peasant woman crosses herself at the sight of her sovereign. A butcher’s boy on an errand stops and gawps.

A thickset clean-shaven man steps in front of the carriage. It’s just after 2 p.m. There’s an unmistakable intent in the way he moves. This starlight is endlessly manipulable. I’m bending it so you can see his face up close. You are surprised by its earnestness and youth. It’s an expressive, open face that would suit a young Midwestern farmer, except his jaw is set in grim resolve. His name is Rysakov. He’s clutching a bundle, which he pitches beneath the wheels. It tears the air with a crack that hurts our ears. Grit and ice and blood spatter onto the slushy road.

As the smoke clears, there’s an eerie pause, a rip in the fundamental story. Busily, people swarm back into action, like ants repairing a ruined nest, rushing, swearing, shouting ‘Treason!’, ‘Catch that man!’ and ‘God save the Tsar!’

One of the Cossack horsemen and the butcher’s boy lie dying in the street. Rysakov is being held. A crowd is forming round the Tsar’s carriage, which is damaged, but he emerges unhurt.

That’s Alexander II – the Tsar liberator, who freed the serfs. He’s sixty-three, tall, moustachioed and rather fine-looking. He’s wearing a furred coat over a military uniform. From one of the sleighs that is following the carriage, Colonel Dvorzhitsky steps out. He urges the Tsar to leave the scene. The crowd is sympathetic, outraged, but the atmosphere is still pregnant with threat. How tentative and panicky everything seems, how different from the fixed lines of history in retrospect.