Zan also staggered – but Gadreel grabbed him, the Nephilim prepared for the sudden shift. He muttered something. Zan hurriedly tugged a cloth-wrapped object from his pocket and gave it to him.

The truth came to Nina: Zan was Eleanor’s spy, selling his intimate knowledge of the Nephilim and their technology in the hope of finding wealth and freedom outside China. The Millers would eventually expose him as a traitor under interrogation – so he had turned to the only person who could now help him escape.

Zan must have taken the object from the archive. What it was, and what Gadreel meant to do with it, she had no idea. But it was also her only way out: the only way she could protect her family from Colonel Wu.

A rumbling sound echoed through the chamber. Nina looked towards the windows – and saw the packed earth outside shifting, slowly sliding over the crystal.

The fortress was moving, the entire structure burrowing up through the thousands of tons of dirt and debris that had buried it for millennia.

Hui had only just recovered from the shock of the quake when the ground trembled again, less violently – but more insistently, the tremors like the thrum of some giant machine.

Which, she realised, might just be the cause. ‘It’s the fortress!’ she shouted. ‘We need to move!’

She ran for the helicopters. Both aircraft were parked well clear of the domed hill, but still shook, rotor blades flapping and bouncing. Wu recovered and chased after her, the soldiers following as the earth began to slide away underfoot.

A hole opened up before Wu. She almost fell into it, but leapt the widening gap just in time. Behind her, a great ragged cleft tore the hillside apart.

Hui finally reached the bottom of the slope and risked a look back. To her shock, she saw that the hill had grown, its summit rising. She ran faster, hearing panicked cries from the soldiers behind—

One shout became a scream as a man was swallowed by an opening crevice – only to be silenced as tons of dirt rolled over him.

Wu Shun cleared the mound and raced after Hui, enmity forgotten in her fear. ‘What’s happening?’ she cried.

‘The fortress,’ Hui panted in reply. ‘It’s coming out of the ground!’

‘How? How is that possible?’

The scientist’s reply was cut off by a roar of falling rubble as something pushed up through the hill – and continued skywards, the dark shape masked by a cascade of sand and stones. A soldier who had just reached level ground was crushed by a churning wave of falling debris. Another man further back was caught in the landslide and plunged with it over the rising edge, screaming all the way down before vanishing into the chaos.

Dust gushed around the two women, who shielded their faces. The landslip’s fearsome noise reached a crescendo . . . then faded.