‘A very rich and unpleasant one,’ said Nina. ‘Mind you, her son did leave her to die from poison gas, so even if they get out of here, I’d imagine the family Christmas dinner would be kinda awkward.’ She gave the other archaeologist a penetrating look. ‘Are they going to get out of here?’

Hui wore a headset to communicate with the base; suddenly uncomfortable, she muted the microphone. ‘That is . . . unlikely,’ she whispered.

‘And what about me and my family?’

The Chinese avoided Nina’s gaze. ‘I will do everything I can to help you. But . . .’

‘But Colonel Wu’s in charge, right?’

A shamefaced nod. ‘Yeah.’

A shout from the pit drew their attention. A soldier jabbed into the soil with his shovel, each strike producing a metallic thunk. An order from the colonel, and the other men converged, working at a more hurried pace. ‘They’ve found it!’ said Nina as a dark grey plate was revealed beneath the dust of ages.

Gadreel, makeshift cape flapping in the gritty wind, stood with the Wus and Zan observing the excavation. He spoke, the translator passing on his words. ‘He said the fortress was buried to hide it from the Shangdi, but there is a way inside. We will have to dig to find it,’ Hui told Nina.

‘That’s one good thing about involving the military, I guess,’ the redhead replied as the soldiers tore into the surface. ‘When they’re told to dig, they dig – no standing about drinking coffee or posing for selfies.’

The other woman smiled. ‘I can tell you have worked with students.’

The hole grew steadily larger. Gadreel spoke again once enough metal had been exposed for him to assess where it sat on the fortress’s exterior. Nina noticed he was no longer addressing Zan directly; rather, he made proclamations and expected the Chinese man at his side to pass them on to everyone within earshot as if he were a medieval herald. Colonel Wu glared at the pair, then gave stern instructions of his own. The men concentrated their digging in a new spot. ‘I don’t think the colonel likes anyone challenging his authority,’ Nina whispered to Hui, faintly amused.

Something else was soon found. As more of the metal surface was uncovered, it was revealed to be curved, matching the domed shape of the hill – but the soldiers now reached a flat-floored recess cutting into it. They quickly cleared it of dirt, exposing what lay at its end.

A door.

It was oval, much taller than it was wide, like the entrance to the icebound fortress. This one, however, was closed tight to protect whatever awaited inside. The only feature on the otherwise smooth surface was a disc inset into its centre.

Nina knew what it was. ‘It’s like the lock on the vault from Turkey,’ she said. ‘It channels earth energy.’ She addressed Gadreel. ‘Am I the only person who can open it?’