As they walked, it was the filth that struck Saladin. All the narrow streets just ran with human sewage. And butchers worked out in the street, making the cobbles a mess of offal and bone fought over by rats and crows and bloody-handed urchins. Though squads of beadles, under-beadles and rakers swept gutters and drains clear of dung and hauled animal remains to the rivers for dumping, the stench of ordure and blood was overwhelming.

But, noisy, crowded, jostling, swaggering, stinking London bustled with commerce. In Jerusalem, tension simmered and arms and armour were everywhere. This sprawling city seemed to be run by merchants and shopkeepers, not by soldiers.

And there were no Saracens here, so Saladin’s dark colouring stood out. A gang of well-dressed young men spotted Saladin and thought him a Saracen himself. ‘Do you eat babies? Do you screw your mother? Get back where you came from, carpet-biter!’ Thomas Busshe restrained him before he could draw his sword, but Saladin seethed.

That night he tried to sleep in air so dense and smoky he could barely breathe. He longed for the hot light of the Outremer, the iron scent of the desert.

In the morning, in Thomas’s priory, they spoke of the fall of Jerusalem.

Joan bit into the tough bread softened by a bit of broth that passed for food here. ‘Well, in the end we had to flee. We all did. Emperor Frederick’s truce expired even before your visit two years ago, Thomas. But the Muslims were squabbling among themselves: brothers, rival princes in Damascus and Egypt, waging war on each other. That saved us for a bit. But at last, this year, one victorious princeling allied himself with the Khorezmians of Syria and took back Syria and Palestine, and - well. Reunited, the Muslims regained the Holy City too.

‘We had warning. We fled with what we could carry, which was little enough. In Acre we bought our way onto one of the last ships - hideously overcrowded, you can imagine. The cost was obscene.’

Saladin was impatient. ‘You talk of money, mother. What does money matter? This was not Saladin, not honourable. These Saracens burned the Church of the Holy Sepulchre. They massacred our people!’

Joan nodded, weary, grim, looking older than her thirty-two years. Saladin thought her experiences had hardened her, that she had come to hate the Saracens as perhaps she had not before. ‘My son would have stayed to fight. I forced him to flee with me, for I needed his protection. Any shame in our flight is mine, not his.’

‘Yes.’ Thomas looked at Saladin. ‘And this is what you must tell your confessor.’

Joan said, ‘So Robert’s blood descendants return to England half destitute. I may yet need the charity of your house, good brother.’

Thomas touched her hand. ‘It won’t come to that. Put away your despair; cling to hope. Your fortunes will rise again . . . I have news for you.’