Martin Scorsese says his next film, Killers of the Flower Moon, feels like a Western — a genre he’s never done before, despite a deep love of Westerns.

The film, based on the nonfiction book by David Grann, describes how the members of the Osage American Indian tribe in Oklahoma became extremely rich when oil was found on their land. But then a series of murders began, and the FBI came in to try to solve them. Leonardo DiCaprio and Robert De Niro will star in the film.

“We think it’s a western,” Scorsese told Cahiers du Cinéma, as reported by Premiere. “It happened in 1921-1922 in Oklahoma. They are certainly cowboys, but they have cars and also horses. The film is mainly about the Osage, an Indian tribe that was given horrible territory, which they loved because they said to themselves that Whites would never be interested in it.”

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He continued: “Then we discovered oil there and, for about ten years, the Osage became the richest people in the world, per capita. Then, as with the Yukon and the Colorado mining regions, the vultures disembark, the white man, the European arrives, and all was lost. There, the underworld had such control over everything that you were more likely to go to jail for killing a dog than for killing an Indian.”

Scorsese’s The Irishman was shut out at the Oscars despite wide praise and 10 nominations. That film was a look back on his past gangster movies, and an attempt to remove any mystique from crime movies by showing how murder hollows out the souls of those who commit it.

But Killers of the Flower Moon, like The Last Temptation of Christ, The Age of Innocence and Silence, will be a dramatic departure from the genre for which Scorsese is best known — especially to those with only a casual knowledge of his filmography.