David Grann must be the only writer who can boast that back-to-back books are being made into films by Martin Scorsese and Leonardo DiCaprio. He says the trick is making incredible facts seem "plausible".
"Killers of the Flower Moon", a true-life tale of murder and exploitation among the Osage Native American community in 1920s America, comes to cinemas and Apple TV in October, having already received rave reviews from its premiere at the Cannes Film Festival earlier this year.
Grann wrote the book and says he loves Scorsese's adaptation, which stars DiCaprio and Robert De Niro and takes a different focus.
"The Osage were deeply involved in the production. That's what makes the movie so powerful. It's shot on location, in the very places where this occurred," Grann told AFP during a visit to Paris.
Before it was even finished, Apple had already bought the rights to his next work, "The Wager", for Scorsese and DiCaprio to adapt.
It promises to be an expensive affair since it tells the astonishing story of a British ship, HMS Wager, that faced a mutiny and was wrecked off the coast of South America in 1741.
These are not his first adaptations. Previous stories have been put on screen, including another South American tale, "The Lost City of Z" and the story of a polite, elderly bank robber, "The Old Man and the Gun" which starred Robert Redford.
Grann goes against the grain of much contemporary non-fiction, leaving himself totally out of the narrative.
For his latest book, that meant leaving out his own adventure to Wager Island in Chile, where he saw the remains of the ship.
"I don't write about my own trip because I felt it would have been an intrusion. And yet, that trip was so essential in all my descriptions, and to bring life to them," he said.
The castaways spent five winter months on this wind-blasted island at the end of the world, starving and cold.
That anyone survived this barren place of rocks, swamps and steep cliffs is barely believable, so Grann felt no need to exaggerate.
In fact, he said, the hardest part was making the truth "look plausible".
"There is a lot of tedium about doing the research. But the fun is when you come across things that make your jaw drop," said Grann, who is a staff writer for The New Yorker.
One such element was a moment he discovered in the original journals—which have miraculously survived—when the ship lost all its sails in a hurricane as the turned Cape Horn.
They had already suffered outbreaks of typhus and scurvy by this point, but now the captain's only solution was to make the crew climb the masts, cling to the ropes and use their bodies as sails.
"I mean, you couldn't make that up, right?" said Grann.
"If they find the right story, people like to take liberties. I'm like, no! Why would I take liberties? So many things are happening," he added.
There was still a job to disentangle the facts from the myths that accumulated later around the story.
"In exploring the facts, you have to explore how they give way to the legends," Grann said.