She glared at him. ‘Stapper said nothing happened until after they put the key in there!’

‘What could happen?’ said Vorster. ‘You said this thing is over a hundred thousand years old. Even if they called it a key, it can’t be like a car ignition key. They didn’t have engines back then.’

‘Not as we know them, no,’ Nina said. ‘But the Atlanteans used something called earth energy – or ley lines, feng shui, song lines, probably a dozen other names – as a power source, and crystals and a type of purple stone to channel it. And gee, look what we have here!’ She pointed at the circles of said materials set into the altar.

‘But this is older than Atlantis, isn’t it?’ asked Imka.

‘Yeah, but it’s the same kind of technology, if you can call it that. In the Turkish vault, the Atlanteans said it came from “those who came before”; I think this was built by the same people. They discovered the power, and the Atlanteans later used it as well. Which ultimately caused them to end up at the bottom of the ocean, because they couldn’t stop fiddling with things they didn’t fully understand.’ She directed that last at Cheng, who averted his eyes.

‘Nina,’ said Eddie from the front of the chamber. ‘There’s something else down here.’

‘What is it?’

‘Buggered if I know. You’re the archaeologist!’

‘Put this away,’ she ordered Cheng, thrusting the key at him before joining her husband. He was partway down the treacherously steep new stairs, shining his light downwards. ‘It’s another room,’ he went on, ‘but . . . well, see for yourself.’

Nina added her torch beam to his. What she saw below made her gasp.

The new room extended further forward into the fortress’s nose, another oval chamber, forty feet on its long axis. Unlike the other rooms they had seen, this was built – grown? – entirely from crystal, the twin lights reflecting from facets beyond facets.

That was not what had stunned Nina, though. It was what was inside the room.

Coffins.

Towering cylinders of metal and crystal stood near-perpendicular to the floor, arranged in concentric rings. The one at the centre was the largest and most elaborate, all the others facing it. The sarcophagi were occupied, huge shadowy forms visible through the translucent covers.

The bodies had not been protected from the ravages of time, however. There were gaps in the rings, missing teeth leaving broken roots where they had stood. She redirected her flashlight. Several sarcophagi were piled amongst debris at the room’s bottom end, cracked and broken. They had torn free and smashed into their companions when the iceberg rolled over.

But the majority of the ancient coffins were intact. The builders of the fortress were still here, preserved.

Eddie flicked his light at the nearest. ‘This one’s open.’