In the 1920s, the Osage Nation in Oklahoma found themselves the wealthiest people per capita due to the oil beneath their land. This ceaseless prosperity, however, marked the beginning of a series of ghastly murders that would later be known as the Reign of Terror. Relative after relative of Osage woman Mollie Burkhart fell victim to ruthless killings as figures of authority and institutions failed to safeguard the Osage community. The mounting casualties finally drew the attention of the FBI, embroiled in its infancy under the direction of a desperate J. Edgar Hoover. Grann unveils the dark underbelly of American history, where Tom White, a former Texas Ranger, and his undercover team, painstakingly unearth a chilling conspiracy against the Osage, driven by insatiable greed and racial injustice.