Nash cleared his throat. ‘Isn’t it time you told me what this is all about?’

WHUMP!

Nash’s head snapped brutally back as Boerman’s punch took him full in the face. Hands tied, head spinning, Nash staggered. Before he could fall, Boerman grabbed him by the shirt and shook him violently.

‘So, Mr fucking know-it-all wants an explanation, does he?’

‘That will do, Jaap.’

Sura sounded satisfied, and Nash knew it was payback for humiliating her on the ship. He spat out a mouthful of blood and ran his tongue around his throbbing lips. At least he still seemed to have his teeth.

‘We’re here for a submarine, Mr Nash.’ Her exhilaration was eerily disembodied in the near darkness. ‘A Japanese megasubmarine that moored in this cave more than seven decades ago and later sank. Somewhere down there is 200 million dollars’ worth of gold bullion, and you’re going to get every last bit of it out!’

‘A submarine . . . here?’

Nash’s astonishment turned to dread. If the Octopus had been a failed test . . . the flooded, rusted hulk of a submarine would be the ultimate examination of his shattered nerve.

Dont be a fool, he chastised himself, remembering the topography of the gorge outside. Sura was completely nuts. No submarine had ever reached this cave. It was physically impossible.

Sura’s focus shifted to Boerman. ‘Why would it sink after so many years on the surface?’

The Afrikaner played his torch over the severed hawser.

‘When the water level in here dropped, the submarine must have tipped. With a stern hatch open, it would pour inside and fill her up fast.’

‘And the cable snapped from the extra weight?’

‘Ja, sent her straight to the bottom.’ He paused to hopefully play his torch into the depths again. ‘With a bit of luck, we’ll be able to use the same hatch to swim straight inside.’

To Nash it sounded fantastical. While their confidence suggested they were in possession of compelling information, the physics simply didn’t allow it. Water found its own level; thus, if you transposed that high-water mark outside the cave, a vast lake would have filled the whole gorge. And there was no way the fall to the Sepik allowed this. He figured the explanation was something to do with the cave mouth. Once, it must have been higher, possibly from a rockfall, which, of course, rendered the whole idea of sailing a submarine up that narrow steep gorge even more ridiculous. As for the hawser, the most likely explanation was that the Dutch had winched equipment into the cave.