I stopped, my hand resting on the door. She was baiting me, I could tell by the way her words rose at the end mockingly. She wanted me to ask. Which was exactly what made me not want to ask. Except I probably ought to. Pettiness wasn’t the right hill to make my stand on in this war.

I turned around and gave her what she wanted. ‘What do you mean, the next wall?’

‘The one around the prison where the traitors have been sent.’ She looked all too pleased with herself now she had regained the upper hand, knees pulled up to her chin. There was an annoying singsong quality to her words when she asked, ‘Where do you think my father got the idea to protect our city this way?’

Ashra’s Wall. The story had leaped into my mind the moment I’d seen the great barrier of fire. And I wasn’t alone in that. Everyone had been whispering Ashra’s name around the city since we saw the wall of fire. It was impossible not to think of the legend from the Holy Books. But there was no way Leyla was talking about that. Because that would mean Ahmed and the others were being kept prisoner in …

‘Eremot.’ Dark satisfaction was scrawled all over Leyla’s face. ‘They’ve been sent to Eremot.’

The ancient name sent a feeling of wrongness through me, an unease that went deeper than my skin and bones and seemed to churn even my soul into unrest. Half of me was immortal. Half of me had been there, at Eremot, in the ancient days. Half of me remembered.

Eremot was a name that belonged in the Holy Books. It was the place where the Destroyer of Worlds had emerged, leading her army of ghouls, and the place she had been imprisoned again at the end of the First War. Behind Ashra’s Wall, a great barrier of fire to keep the dark at bay.

‘Eremot is …’ not real. Only that wouldn’t get past my lips.

‘The stuff of legends,’ Leyla finished for me, with a pinched, self-satisfied look on her face. ‘Past the end of civilisation where no one can find it. But I found it.’

She meant to intimidate me. But I’d grown up past the end of civilisation and Jin had found me just fine. ‘We’ve got our own ways of finding it.’ Jin’s compass would lead us to wherever the prisoners were being held. Whether that was Eremot or not.

‘Well.’ Leyla shrugged. ‘Even if you do find it, do you really think you can cross a great and impenetrable barrier against evil, risen from the trueness of sacrifice and which—’

‘And which will stand un-breached until such time as humanity’s courage fails,’ I finished for her. ‘I can quote the Holy Books, too, when I want to.’

Ashra had been a carpet weaver’s daughter born when the First War was coming to an end. The ghouls were being driven into hiding and darkness, skulking the desert alone at night instead of swarming in armies. The Destroyer of Worlds’ greatest monsters were dead, slain by the First Hero and all the heroes that came after him: Attallah, the Grey Prince, Sultan Soroush, and the Champion of Bashib. The Destroyer of Worlds was being beaten back to the darkness of the earth from whence she came.

But she could not be held back permanently. Each time, she burst free from her prison again to roam and terrorise the desert. And the Djinn looked on in despair at the humans who had defended them for so long and feared that they would not be able to accomplish this final task. So they made it known among the humans that they would grant immortality to whichever man could imprison the Destroyer of Worlds forevermore. Many a hero died trying.

Ashra was not a hero. She was just a girl from a small village in the mountains, the eldest of twelve children, who spent her days helping her father dye wool and her evenings helping her mother cook meals for her eleven brothers and sisters.

Until the day the Destroyer of Worlds came to her village.

The villagers had no weapons, and they lit torches against the Destroyer of Worlds, placing them in a circle as they huddled together, trying to stay alive until dawn, when they would be able to flee.

The Destroyer of Worlds stalked through the dark in one great circle around the village, around their torches. And then she laughed, and with her breath she extinguished all the torches. All except one, which stood by Ashra and her family.

Before the Destroyer of Worlds could attack, Ashra seized the last torch and set herself on fire with it. A body does not burn much, but it was said that she swallowed a spark, just enough to light her soul as well as her body. And her soul burned much brighter than her body ever could. And when the burning girl took a step towards the Destroyer of Worlds, the Destroyer of Worlds took a step back. So Ashra took another step, then another, and another, and slowly the Destroyer of Worlds retreated.

Ashra walked the Destroyer of Worlds all the way back towards Eremot. And as she walked, she did as her father had taught her and wove the fire burning inside her body together, as one would a carpet, until it became an impenetrable wall. By the time they reached Eremot, she had made it so high and wide that it held back even the Destroyer of Worlds. It was wide enough to encircle the entrance to Eremot and keep the Destroyer of Worlds trapped inside the mountain forever.

The Djinn saw her sacrifice, and they kept their promise. They granted Ashra immortal life so that her soul would burn forever as the great wall she had made. They said that as long as Ashra’s Wall stood, the Destroyer of Worlds would be imprisoned. If it fell, so would a new age of darkness fall on the world.

So that was why Leyla had asked if we were headed to rescue Rahim. Not because she had had a change of heart about her brother, but because she wanted to know for sure that even if she betrayed her father and let us through this wall, we would still fail. There was another wall between us and our purpose.