In 1836, two missionaries and their wives were among the first Americans to cross the Rockies by covered wagon on what would become the Oregon Trail. Dr. Marcus Whitman and Reverend Henry Spalding were headed to present-day Washington state and Idaho, where they aimed to convert members of the Cayuse and Nez Perce tribes. Both would fail spectacularly as missionaries. But Spalding would succeed as a propagandist, inventing a story that recast his friend as a hero, and helped to fuel the massive westward migration that would eventually lead to the devastation of those they had purportedly set out to save. As Spalding told it, after uncovering a British and Catholic plot to steal the Oregon Territory from the United States, Whitman undertook a heroic solo ride across the country to alert the President. In fact, he had travelled to Washington to save his own job. Soon after his return, Whitman, his wife, and eleven others were massacred by a group of Cayuse. Though they had ample reason - Whitman supported the explosion of white migration that was encroaching on their territory, and seemed to blame for a deadly measles outbreak - the Cayuse were portrayed as murderous savages. Five were executed. This fascinating, impeccably researched narrative traces the ripple effect of these events across the century that followed. While the Cayuse eventually lost the vast majority of their territory, thanks to the efforts of Spalding and others who turned the story to their own purposes, Whitman was celebrated well into the middle of the 20th century for having ''saved Oregon.'' Accounts of his heroic exploits appeared in congressional documents, The New York Times, and Life magazine, and became a central founding myth of the Pacific Northwest.