The chopper’s occupants disembarked. Everyone moved clear of the aircraft, regrouping nearby. ‘Okay,’ said Nina, surveying their surroundings, ‘what have we found?’ They were in the mountains’ foothills, a cold wind blowing down the rocky slopes. The sprawl of Xinengyuan began several miles to the south, past nothing but desolation. There was no need to worry about keeping civilians away; there was nobody else remotely nearby.

‘He says the vimana, the fortress, is here,’ Zan announced, also looking around. ‘But I don’t know where.’

‘He does,’ said Wu Shun, the young woman striding to Gadreel. He was almost twice her height, but she put her hands on her hips like a teacher sternly addressing a pupil as she spoke to him. Zan translated. The Nephilim gave Wu a disdainful look, then turned to the nearby hill, speaking again.

‘He says it’s here, under the hill,’ Zan announced.

Nina regarded the rise. It was roughly eighty feet at its highest, a near-symmetrical mound of sand and broken rock perhaps a hundred yards across. The fortress from the iceberg could have fitted into it several times over. ‘Hope you brought shovels, because you’ll need to do a lot of digging to find it.’

Even though Gadreel could not have known exactly what she said, he still picked up the gist from her tone. The towering figure smiled, the expression disturbingly out of place on his not-quite-human features, then said something to her.

She looked back at Zan. ‘What did he say?’

‘He said,’ the translator replied, ‘it will not be hard to find. It is not buried underneath the hill.’ His eyes widened in surprise. ‘It is the hill!’

Gadreel directed the group to one side of the mound, climbing roughly halfway up it. The soldiers from the second helicopter had indeed brought digging equipment; Colonel Wu waited for Zan to relay the Nephilim’s instructions, then ordered his men to start excavating.

The hill’s upper layers were little more than sand and scree, the soldiers making rapid progress, but before long the ground became more densely packed. Even so, with so many people working hard, a large hole was soon opened up. Four feet deep, five, six, the crater widening.

Nina stood near the edge to watch. Assuming Gadreel was right and the fortress was indeed here, how deep down would it be? The passage of over a hundred millennia could have deposited an awful lot of debris upon it . . .

Major Wu took a phone call, then spoke to her father. The colonel’s response was simultaneously satisfied yet impatient.

‘What was that about?’ Nina asked Hui.

‘They think Eleanor Miller will soon tell them the name of the spy,’ she replied, before shaking her head. ‘What sort of woman would let her son suffer to protect a secret, but break because her money is being taken away?’