‘I don’t know,’ Bekker said, misgivings growing. Assuming this wasn’t some dumb joke by the climbers – and he didn’t think their acting ability was up to it – then they had found something unknown. And the unknown could be dangerous. ‘Take pictures, then come back. We need to see what we’re dealing with.’

‘No, no, it will take two minutes to climb to the door,’ replied Stapper. ‘We can’t come this far and not look inside!’

Frustrated, Bekker looked to Havman for support. ‘If they were my crew, I would order them back,’ said the captain. ‘You are their boss.’

‘Yeah.’ He spoke into the radio again. ‘No, get back here. Or . . .’ He halted, aware there wasn’t anything he could threaten them with short of being fired, and then the expedition would be over before it even began. ‘Just get back to the ship.’

The lack of a response meant the pair were either ignoring him, or already climbing the ice wall. ‘Pielkop!’ he muttered.

The walkie-talkie remained silent for a few fraught minutes, then crackled to life. ‘We are at the door,’ said Stapper at last. The distortion was worse than before. ‘It’s big, nearly three metres high. It opened when Sanna touched a round thing on it. We’re going in.’

Bekker sighed in resignation: they were entering with or without his permission. ‘If there’s any danger, get out and come back to the ship.’

‘We will. But the ice is solid. I don’t think—’

The Dutchman was abruptly cut off by a harsh caw of static. ‘Wim?’ said Bekker. ‘Wim, can you hear me? Wim!’ No answer. ‘Shit!’

Havman marched to the helm. ‘I will bring the ship closer. If they are in trouble, we can reach them faster.’

‘Good, okay,’ Bekker replied, before trying the radio again.

There was still no response.

‘Why did you let them go in?’ demanded Imka Joubert over the satellite link. The video quality was low and glitchy, the computers at each end straining to make the most of the parsimonious bandwidth.

‘I told them not to!’ said Bekker. Thirty minutes had passed since his last contact with the explorers; he had called his fiancée as much to vent about the situation as report on it. ‘This is what happens when you hire thrill-seekers – they go seeking thrills!’

‘When I hired them?’

‘Okay, when we hired them! But we lost contact when they went inside this thing, and still haven’t heard anything from them.’

‘What is this thing?’ Imka asked. ‘What did you find?’

‘I don’t want to say on an open channel. Let’s call it an . . . old ship.’

‘What, like a sailing ship?’

‘I’ll tell you more when I can set up an encrypted link.’

A disbelieving laugh. ‘You really think anyone is eavesdropping?’

‘I don’t want to take any chances. Trust me, Imka.’