On April 18, 1983, someone drove a van packed with explosives into the United States embassy in Beirut, demolishing it and killing 63 people. Six months later, 241 Marines and soldiers were killed when their Beirut barracks were torn apart by a truck carrying 12,000 pounds of dynamite, which detonated the largest nonnuclear explosion since World War II. The twin suicide bombings shocked and intrigued Robert Baer, who at the time was stationed in Lebanon as a Central Intelligence Agency officer and knew several agency employees who had died in the embassy. He became preoccupied with who had plotted the...