Nash found his father’s ambivalence towards his old naval buddy intriguing. Sure, he was rough around the edges, but hadn’t Douglas always looked out for him? For example, the selection trials at his cricket-mad junior school. Nash was an athlete but struggled with ball sports. After a week of Uncle Frank’s tough love – a hail of bouncers and yorkers – he’d managed not to embarrass himself and even ended up playing for the second XI.

‘Dad, you gave me the same advice five years ago, remember?’

‘True, but that time you were running the show, and there were twenty other people looking out for you. All I’m saying is don’t be too reliant on him. Watch your back. If you don’t like the look of something, use your instincts and get the hell out of there. Understood?’

‘Yeah, sure, Dad. I’ll do that. Love you.’

It struck Nash that he had always taken his parents’ support for granted, a birthright for the golden boy. Recalling their farewell at the airport – his father’s frailty, his mother’s sadness, Jacquie’s strained optimism – he realised they must have felt like that every time he’d embarked on a major dive.

It was dawn on the fourth day when they reached Broken Water Bay in the Bismarck Sea. Dense, white mist obliterated the river mouth, ten kilometres distant, but the Sepik’s brooding presence was evident in the brown water beneath their keel. Kaboro slowed the boat to ten knots and warned his men to look out for trees and other detritus.

The rising sun began clearing the mist, revealing a well-defined river mouth, a kilometre and a half wide, fringed by a low jungle of mangroves on each side. Kaboro handed Nash the binoculars.

‘There is no delta,’ he explained. ‘The river flows fast, and the sea floor drops steeply.’ He indicated a chart showing they were travelling over a vast submarine canyon, bisecting the narrow continental shelf, a feature which swallowed the endless sediments washing down from the mountainous interior. ‘There is a shallower bar one nautical mile upstream,’ Kaboro added. ‘But it won’t be a problem for us – even this late in the dry season.’

As the river narrowed, the gnarled mangrove sentinels guarding the coast gave way to vast swampy flood plains of impenetrable sago forest. Even at this early hour, it was stiflingly humid. Only the raised riverbank levees and the occasional low hill studded in small trees resembled anything like terra firma.

Frank Douglas joined them as they passed a settlement of thatched huts perched precariously on rickety timber legs. A lone naked man in a hollowed-out wooden canoe watched impassively from the shallows. Wisps of steam rose from the river’s surface and hung primordially about him like ghostly streamers.

‘It’s like going back in time,’ marvelled Nash.

‘Yeah, the Stone Age.’ Douglas spat over the side.