She put the thought aside – for now – as she continued around the curving corridor. There were more signs of damage, ice forming on the walls where the floor had buckled. She examined a rent between two frozen panels. One of the crystal ribs had been snapped by the ice’s relentless pressure. The material wasn’t indestructible, then. Had the intact crystals somehow held back the frost?

The passage ahead angled downwards towards the front of the fortress. ‘It’s getting steep again.’

‘Think we’ll need ropes?’ Eddie asked. He shone his torch down the corridor. Metal and crystal glinted in the cold darkness – together with something else. Warning entered his voice. ‘Everyone hold back.’

Standing out on the golden sheen of orichalcum was a darker splash, as if paint had been splattered over the walls and floor. At first glance it looked black, but as Nina’s flashlight beam joined his, they saw with dawning horror that it was actually a deep red.

Blood.

‘What is it?’ Imka asked, trying to peer around the couple.

‘Wait here,’ Eddie said firmly. ‘I’ll have a look. Cheng, Janco, hold onto my rope.’

He handed the coil to the two men, who braced themselves behind him. Nina knew what her husband was doing – blocking Imka’s view of what they both suspected he was about to find. He gripped the rope, then moved carefully down the steep slope.

Eddie soon reached the marks and played his torch over them. Bone fragments and shreds of flesh amongst the frozen blood confirmed his fears. Someone had been caught in an explosion, almost liquefied by the blast.

But what had caused it? To obliterate a human body so completely would need far more explosive than found in a hand grenade – which would also have ripped the passage apart. But there was no visible damage to the walls . . .

‘What have you found?’ Imka called.

‘Someone was killed here,’ he reported grimly. ‘Looks like there was an explosion.’ He aimed his light further downwards. ‘Shit,’ he whispered, seeing another dark burst twenty feet away. Gruesome confirmation that the remains were human came in the form of a booted foot wedged against a crystal rib, shards of bloodied bone jutting from it. ‘There’s another body – or what’s left of one.’

‘Oh . . . oh my God,’ said Imka. ‘Is it . . . is it Arnold?’

‘I don’t know.’ She had shown them pictures of her fiancé during the voyage, but Eddie saw nothing here that could be used for purposes of identification short of a DNA test. He shone the beam past the grisly remains. Ice encroached into the corridor beyond a section of mangled wall. ‘I don’t think we can get down that way. We’ll have to go back around past the entrance.’

‘But we need to find out who they are!’ the South African cried.