In 1971 a young French ethnologist named Francois Bizot was taken prisoner by forces of the Khmer Rouge who kept him chained in a jungle camp for months before releasing him. Four years later Bizot became the intermediary between the now victorious Khmer Rouge and the occupants of the besieged French embassy in Phnom Penh, eventually leading a desperate convoy of foreigners to safety across the Thai border.

Out of those ordeals comes this transfixing book. At its center lies the relationship between Bizot and his principal captor, a man named Douch, who is today known as the most...