Nash put his hand on Mia’s arm. ‘We’re out of options.’

Mia flung her arms around him, then Douglas.

‘Goodbye, Frank.’

Nash embraced him, too.

‘Don’t look back,’ Douglas whispered. ‘Fight, run . . . it doesn’t matter – just fucking survive, you hear me?’

In two gleaming yellow piles, the gold bullion was stacked on a blue tarpaulin. It was a production line: Boerman was down inside the submarine, jemmying open the stubborn drawers, passing the precious bars out to a soldier, who placed them in a steel bucket. This was carefully hauled up, ten kilos at a time, through the hole cut in the submarine’s hull, to the sinkhole edge. From there the bars were passed, one by one, along a line of soaking wet soldiers, with Sura and Alatas there to ensure none found their way down a pocket.

Kitted up in his drysuit, Nash watched on with Mia. He sensed their moment was passing. The end of the gorge was invisible in thick grey cloud, and he feared Sura would be unable to fly out.

Making matters worse, she was about to put them to work.

Clutching a walkie-talkie, Sura squelched across in an oversized poncho.

‘The Hoosenbeck has risen a metre in the last fifteen minutes and is close to the lip. You two will be roped down to help salvage the opium.’

Nash exchanged glances with Mia. This was a disaster. Frank would be left fighting on his own, and they would be trapped like rats in a bucket.

‘Take your gear for when it becomes necessary to dive, Mr Nash. Should you attempt an escape, your girlfriend will be shot.’ Sura smirked briefly at Mia. ‘Are we clear? Your fate is in your own hands.’

It was a pantomime; they all knew this woman intended to kill them. Staring into Sura’s disingenuous eyes, Nash realised he was glad that she was going to die. A flicker of something entered her expression – some flash of intuition – and he quickly got back in character and looked down.

‘Yes, perfectly.’

With fingers clumsy from cold and nerves, Nash strapped on his preferred rebreather. Clipping mask and fins to his weight belt, he also decided to take a small pony tank of emergency compressed air. The size of a large vacuum flask, it contained just 540 litres, good for about nine minutes at shallow depth. Its purpose was to allow Mia to hide underwater, because if Sura’s numbers were correct, around sixteen Olympic-sized swimming pools were pouring into the Hoosenbeck Cavern every half an hour, and they were going to be inundated at any moment.

A powered winch had been set up to access the stern of the submarine. There was no harness; they were simply shoved into a cargo net which creakingly lifted them up.