Debuted: April 27 2017

If you’re familiar with The New Yorker writer David Grann’s brand of investigative journalism, as seen in his outstanding 2009 best seller The Lost City of Z, you already know he is relentless and crazy-thorough in his quests to get to the bottom of little-known yet captivating historical mysteries.

You also know that not only does Grann skillfully uncover new breakthroughs, he tactfully — and sometimes dangerously — becomes part of the story.

Grann has applied that high-upside approach in his new book, Killers of the Flower Moon (Doubleday, 338 pp., ***½ out of four stars), a shocking whodunit that probes a sinister conspiracy that resulted in the murders of more than two dozen Osage Indians in Oklahoma in the early 1920s.

At that time, the Osage went, practically overnight, from being one of America’s poorest communities to being among the richest people per capita on the planet.

How? In 1870, when the feds relocated the tribe to destitute prairie land in northern Oklahoma, nobody knew what lay beneath the ground. But a smart young Osage lawyer cut a deal giving the Osage headrights to the property’s oil, gas, coal and minerals. Fifty years later, oil was discovered. The tribe was sitting on a fortune. Oil barons lined up to pay unthinkable prices to drill for oil, and Osage tribal members received their share. Instant millionaires!

Figuring Osage Indians were unable to handle their own affairs, the federal government instituted a guardian system that unintentionally invited corruption. Court-appointed guardians looted Osage bank accounts. Some became beneficiaries to Osage fortunes, then cashed out by committing murders. From 1921 to 1923, at least two dozen Osage Indians died in suspicious ways, including questionable car crashes, faked suicides, explosions,…