The Templars: The Rise and Fall of God's Holy Warriors, Dan Jones

The Knights Templar were the wealthiest, most powerful—and most secretive—of the military orders that flourished in the crusading era. Their story—encompassing as it does the greatest international conflict of the Middle Ages, a network of international finance, a swift rise in wealth and influence, followed by a bloody and humiliating fall—has left a comet's tail of mystery that continues to fascinate and inspire historians, novelists, and conspiracy theorists.