Joan studied him. ‘You’re being enigmatic, brother. Spit it out, man.’

‘Not here.’ He glanced around the empty room. ‘London is a nest of spies.’

‘Even here, in this priory?’

‘Monks must make a living, lady. We must operate in the world of money and power. It’s a corrupting environment. I will bring you to my own house, which is far from London. There we can talk with confidence.’

Saladin groaned. ‘More travelling?’

‘No more ships,’ Thomas said. ‘I promise you that.’

‘But what is it you want to tell us?’ Joan demanded. ‘Give us a hint at least.’

Thomas smiled. ‘Very well. I have come to believe more firmly than ever that your family legend of war engines and prophecies may have some truth in it. For I have stumbled upon evidence that such things have happened more than once. Warnings from the future, leaked into the past. No, not just evidence - I believe, proof. Eyewitness proof.’

Joan and Saladin stared at him. But he would say no more.

The next day they journeyed north out of London, jolting over an old Roman road, not repaired for centuries. Saladin longed for a camel’s smooth gait, but there were no camels in England.

The country was green, and even away from the city the land was crowded, Saladin thought, full of people, carpeted with farms and studded with little towns and dung-coloured villages. Waterwheels creaked by the rivers, and windmills whispered as they turned in the breeze.

They stopped for a night at a city called Colchester. Set above a river, it was surrounded by bristling walls laid out in a vast rectangle, walls founded by the Romans but built up massively by the generations since.

Thomas said the history of England was written in those battered walls. William the Conqueror’s descendants had been a sorry lot, and fifty years after William’s death the country was racked by a long civil war between Stephen and Matilda, two of William’s grandchildren. Thus, said Thomas, the ultimate legacy of William the Bastard: a once-prosperous country ruined by fratricidal warfare, famine, extortion, carnage and chaos. Saladin had heard of Matilda’s grandson Richard the Lionheart. But King Richard died not long after his final crusade. His brother John was a weak, distrustful, treacherous, deeply unpopular king who was forced to cede power to his barons in a Great Charter, and under John’s son, the third King Henry, a council of nobles, called a ‘parliament’, began to meet in Westminster. In England, then, power was shifting. But the latest King Henry favoured the church; great cathedrals sprouted like mushrooms . . .