Set against the romance of revolution and the terror of a military coup, this arresting mystery is also a reckoning with the callousness of U.S. foreign policy. In 1972 two idealistic young Americans, Charles Horman and Frank Teruggi, arrived in Chile to participate in President Salvador Allende's socialist and democratic revolution. A year later they were secretly executed as Chile's military, with U.S. backing, deposed Allende. Following...