‘By the end of the next day,’ Thomas said, ‘the Great Khan was doubled up in pain. His vomit was copious, while bloody diarrhoea hosed from his leathery backside. His doctors could do nothing. By the following morning he was unable even to pass water, and howled in agony. And by the end of the day after that he was dead. It was a horrible death - but not as dreadful as that inflicted on Brother Bohemond, who was discovered skulking in the Khan’s tent.’

Like many of the other embassies, the Christian party packed up and fled in haste from the decapitated court. The Mongols’ own messengers spread the news of the Khan’s death to the generals and governors across their scattered domains.

‘And that is why,’ Thomas said, ‘early in the year 1242, rather than press his conquest west, Sabotai turned back from the walls of Vienna. For all their conquests the Mongols remain tribesmen, bound by oaths of loyalty to their Khan. So when Ogodai died, their leaders were forced by their own laws to return in person to their homeland, to elect a new ruler.’

‘And will they not return to Europe?’ Saladin asked.

‘They haven’t yet. They have the rest of the world to occupy them. And as for the amulet - after the envoys had fled from the Mongol city, Philip told me they finally shattered its casing with rocks. Inside they found not the shrivelled corpse of an imp, but bits of wire. Metal discs, like coins, but blank. Other strange little sculptures.’

‘Charms, perhaps,’ said Saladin.

‘Philip thought they were like bits of an engine. But what its function could be, how it worked - even what drove it, for there was no spring, no lever - he had no idea.’

Joan said, ‘But whatever it was, why was this amulet put into the luggage of this boy Bohemond?’

‘I think that’s clear enough. It was put there so Bohemond should kill Ogodai. If he had lived, Christendom was lost. If he died, Christendom was saved. As simple as that. So he had to die.’

‘But who could know this? . . . Ah,’ Joan said. ‘A prophet. Or—’

‘Or a meddler with time,’ Thomas said. ‘A Weaver. A man, or an angel or a demon, with the power to speak to the past. A man stranded in this dismal future wrecked by the Khans, who managed to send back this imp-in-a-box - just as somebody, somewhere, somewhen, sent back - perhaps, perhaps! - the designs of your war machines to a young boy’s addled head, and somebody else sent al-Hafredi back to the time of Charles Martel, and somebody else whispered in the ear of your ancestress Eadgyth, and, and . . .’

‘But this was not the work of al-Hafredi’s people.’