Under the Banner of Heaven, by Jon Krakauer, tells the story of Ron and Dan Lafferty, two Mormon fundamentalists who killed their brother’s wife and her infant daughter. They admitted to the crime, and they even justified it, claiming that they were following God-given orders to kill the woman and child.

They believed they were following God’s orders, and Krakauer uses the book to shed light on the reason they believed this. Krakauer begins by telling the story of the murders—murders committed by the Lafferty brothers because their sister-in-law Brenda resisted the ideas of the Mormon Church—particularly the endorsement of polygamy. She also encouraged Ron and Dan’s wives to resist polygamy—and as a result of her interference, Ron believed, his wife left him when he made the decision to take another wife.

After telling the story of the murders, Krakauer relates the history of the Mormon Church and the philosophy of Joseph Smith, who believed that people who believed in the Lord could receive divine revelations.

He traces changes in Ron’s behavior to his understanding of the ideas of Mormon fundamentalism, however misguided. In fact, Ron goes to trial and is diagnosed with a mental disorder. Nevertheless, Krakauer links the ideas the Laffertys used to justify their Lafferty’s crime to Mormon fundamentalist teachings, specifically the teachings that endorse polygamy.

The book weaves together the facts of the case with the history of Mormonism, creating a unique look at both the past and present of one of America's largest religious sects.