Wintz had made quick progress across the cliff, clambering around the outcrop towards the rope ladder. But she was more concerned with her immediate surroundings. The ledge was littered with fallen chunks of ice. Looking up, she saw cracks weaving outwards from the embedded fortress.

Imka emerged behind her. ‘Look!’ she cried, alarmed.

Nina turned to see that the tremors had set the various chains and lines hanging from the Dionysius swinging. The heavy anchor rolled beneath the ship’s bow like a pendulum. ‘That won’t hold for much longer,’ she said as a man-sized hunk of ice broke from near the stern and tumbled into the water. ‘Get Eddie out, now!’

‘Quiet,’ said Harhund. ‘We may still have time to get another coffin.’

‘Are you kidding me?’ said Nina, but the Scandinavian pushed past her and re-entered the fortress to shout instructions. Roche gave the swinging chains a wary look, then took up position to guard the prisoners.

Wintz reached the ladder’s foot and boarded one of his team’s boats. He brought it deeper into the cave, giving the zone beneath the Dionysius a wide berth as more ice fell from above. He stopped at the bottom of the cliff near the forest of icicles. Naider was still impaled upon one, the blue ice beneath him stained red.

Harhund returned. The situation’s urgency was instantly made clear; he was carrying ropes and ice screws himself rather than delegating the task. ‘Martel, help me,’ he told the second man with them. They started to drive screws into the frozen cliff face as Roche maintained his watch.

Another shudder rattled the cave. The ice around the trapped fortress crackled, a new stress line tearing across it. Nina gasped and shielded her head as debris clattered onto the ledge, a piece striking Martel’s shoulder and making him swear.

The cold hail eased off. She peered up at the new crack, then turned to see if the fortress had suffered any damage.

It had. The already buckled section below the broken window had split wider. A light was visible within, brighter than anything she had seen inside. She worked out its position. Beneath the throne room, behind the mausoleum, under the snake skull’s chin. What was it? Some kind of central focus for the fortress’s power?

Grunts and huffs from the tunnel preceded the coffin’s arrival, the other mercenaries bearing it into the open. Sapphire light glinted from it, unexpectedly highlighting the ancient figure within. Nina moved to let the men carry it past, gazing at its contents. A body so old she would have expected to be desiccated, naturally mummified, but this had held its form. Had the gas inside the sarcophagus preserved it?