In the 1920s, the richest people per capita in the world were members of the Osage 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, the Osage began to be killed off. The family of an Osage woman, Mollie Burkhart, became a prime target. One of her relatives was shot. Another was poisoned. And it was just the beginning,...