She came back to her party. ‘Basically their orders are not to let anybody else into Cathay, not ever again. Because Cathay is full, and there is famine and plague. Orders of the Khan. They speak about incursions all along the frontier. The Khan is sending troops to the north and west to keep down his own wilder cousins. It sounds like it’s a sink of madness out there, where one side builds up a wall only for the other to smash it down again. What this means is that it’s going to be expensive to get past these fellows. Your saving the world is costing me a lot of money, scholar.’

‘Then let me deal with it,’ Pyxeas snapped, impatient. ‘Help me down, Avatak.’ The scholar rummaged in the packs until he pulled out the wreck of his oracle – just the frame, broken open, the little sun and moon snapped off. Now Pyxeas prised at the back of the gadget’s face until a panel popped open, and a small golden plaque fell out into the old man’s hand. Pyxeas handed the ruined oracle back to Avatak. ‘Put this away.’

Then, limping, he approached the guards, who watched him curiously. ‘Here! You fellows at the gate! My name is Pyxeas, scholar of Northland, and no doubt you will recognise this.’ He held up the plaque.

He had spoken in his own tongue. The guards obviously understood not a word. But they stared at the golden plaque, took it, read words inscribed there, their lips moving. They handed the plaque back. They both bowed, murmuring what sounded like apologies, and stood back, opening the barrier as they went.

Uzzia was astonished. ‘How did you do that? Give me that.’ She took the golden disc and studied it.

‘That is my paiza, which is the Cathay word for it; the Mongols call it a gerega. The words are written in Mongol and Cathay scripts. It is a right of passage, a guarantee of safety, given me by the great Khan himself. Not the present incumbent – a predecessor. My colleagues in Daidu requested this, and one of them carried it to Northland for me, some years ago. Are you surprised that I possess such a thing, trader? Are you surprised that I, a Northlander scholar, am held in such esteem, even though I have never visited Cathay before? I tell you they are eager to meet me there, just as I am eager to see them. I suggest we get on with the journey. What do you say?’

She handed back the paiza. ‘Lead the way.’

Once past the wall they came to a substantial community, a sprawling town dominated by another monastery cut into a cliff. In the end they stayed a couple of nights.