Killers of the Flower Moon (Used Book) - David Grann
In the 1920s, the richest people per capita in the world were members of the Osage Indian Nation in Oklahoma. After oil was discovered beneath their land, the Osage rode in chauffeured automobiles, built mansions, and sent their children to study in Europe.
Then, one by one, they began to be killed off. One Osage woman, Mollie Burkhart, watched as her family was murdered. Her older sister was shot. Her mother was then slowly poisoned. And it was just the beginning, as more Osage began to die under mysterious circumstances.