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, they rode in chauffeured cars and lived in mansions. Then, one by one, the Osage began to be killed. Mollie Burkhart watched as her family became a prime target. Her relatives were shot and poisoned. Other Osage were also dying under mysterious circumstances, and many of those who investigated the crimes were themselves murdered.

As the death toll rose, the case was taken up by the newly created FBI and its young, secretive director, J. Edgar Hoover. Struggling to crack the mystery, Hoover turned to a former Texas Ranger named Tom White, who put together an undercover team, including a Native American agent. They infiltrated this last remnant of the Wild West, and together with the Osage began to expose one of the most chilling conspiracies in American history.