Basing his movie on David Grann’s non-fiction book “Killers of the Flower Moon: The Osage Murders and the Birth of the FBI,” director and screenwriter Martin Scorsese creates a masterpiece of filmmaking. Co-writing with Eric Roth, Scorsese devotes more time to the first half of that title than to the fledgling FBI. Yet even with that alteration, the film runs three hours and 26 minutes. Audiences, however, are not restive as this true story from America’s past proves that fact can be more compelling than fiction.

Helping to tell this story is a superb cast of Native American newcomers to the screen, along with legendary award-winning Hollywood actors. The “Flower Moon” refers to an Osage celebration, and they have much to celebrate as the Osage nation, removed from the fertile prairie states to a more barren Oklahoma, are now the owners of hundreds of active oil wells. It is the early 1920s, and statistics indicate that per capita, the Osage are the richest people in the world.

Fearing the Native Americans would not be able to manage their wealth, the Government has assigned money managers to monitor their assets. But the problem that slowly grows is that the Osage have become targeted by unseen forces. By the end of 1921, several tribal men had been shot or blown up on country roads or within their homes, while many Osage women had died slowly of “wasting” disease. Another alarming statistic is that many Osage have been diagnosed with diabetes and are getting regular shots of insulin.

Arriving by train in Fairfax, Oklahoma, now a thriving town at the heart of Osage country, is a young veteran of World War I, Ernest Burkhart (Leonardo DiCaprio), who has come to visit his uncle, William Hale (Robert De Niro), a wealthy cattle rancher known as the “King of Osage Hills” for his generosity in building both a hospital and a school in Fairfax. Ernest is hoping his uncle will help him find him a job.

Uncle William sizes up his nephew and finds him a good-looking young man who might appeal to women. He advises Ernest that his road to wealth would be to court and marry an Osage woman. He then gives Ernest the use of a nice car so that he can become a chauffeur-for-hire. One of his steadiest passengers is Mollie Kyle (Lily Gladstone), a beautiful young Osage woman who chooses to ride with Ernest whenever possible. They flirt with each other, fall in love, and eventually marry.   In the meantime, Mollie’s mother dies of the “wasting disease,” and one of her sisters, the feistiest, is shot.

The mysterious deaths continue, and even national newspapers write about them.  A new Bureau of Investigation has formed in Washington with a young J. Edgar Hoover in charge. Wanting to gain national acclaim, Hoover is willing to spend resources on solving the mysterious deaths in Fairfax County. He hires a Texas Ranger, Tom White (Jesse Plemons), and gives him several deputies to use as undercover agents. The men submerge themselves within the community and are never seen together, meeting only at night in dark, remote places to report to White and to piece together their findings.

Several factors contribute to making “Killers of the Flower Moon” a gripping and compelling movie. Scorsese puts together a remarkable cast, using reliably fine actors like Robert De Niro and newcomers like Lily Gladstone, whose quiet dignity and expressive eyes capture audience sympathy. But perhaps his most important directorial decision was to make a casting change from his original plan to have DiCaprio play good-guy Tom White to switching this appealing actor to play the equivocating Ernest Burkhart. The decision was brilliant, and DiCaprio more than rises to the challenge.

The movie and its cast are sure to get Academy Award attention next year.