Jon Krakauer's latest journey into the external and internal wilderness, Under The Banner Of Heaven, opens with the facts of a 1984 murder case in which fundamentalist Mormon brothers Dan and Ron Lafferty slit the throats of their sister-in-law and infant niece. Krakauer then leaves the crime aside to embark on a tour of fundamentalist Mormon communities in Arizona and British Columbia, describing how polygamy persists in small towns that bilk the U.S. government out of millions of dollars a year in welfare for spiritually wed "single mothers." This prompts a brief recounting of the early history of Mormonism, and from there, Krakauer covers the story of how the religion developed in the 19th century, the timeline of the Laffertys' ritual killing, and other disturbing acts of contemporary fringe fundamentalists. At times, the book's organization seems haphazard, and the detailed accounting of pre-Civil War Mormon/Gentile conflicts seems too dense, but Krakauer's method begins to make sense once names from one section begin popping up in another. In addition to indicating how close-knit the Mormon culture can appear to outsiders, the way family names persist across generations helps make the author's main point: that the Laffertys' decision to slaughter their own relatives was rooted in the history of their faith. Under The Banner Of Heaven connects to Krakauer's bestsellers Into The Wild and Into Thin Air through its contemplation of how harsh landscapes attract and nurture the kind of people who think freely and sometimes wander into dangerous psychological spaces. The story of the book is the story of religion subdividing into infinity, as Christianity moves beyond Judaism, Mormonism moves beyond Christianity, and fundamentalist Mormonism attempts to carry a message of damnation and salvation still further. Krakauer leans heavily on the idea of religion-building as a wrenching act, in order to add more drama to his climactic coverage of Ron Lafferty's death-penalty trial, during which psychiatrists on both sides debate whether anyone who claims to receive divine guidance is inherently crazy. Krakauer follows the implications of those arguments to their end, turning Under The Banner Of Heaven into an understated, unsettling critique of the American pioneer spirit, and the way the charismatic leaders who built the country could be read as simple psychotic narcissists.