From his first day in Vu Quang, a reserve that lies on the mountainous divide separating Vietnam from Laos, biologist John MacKinnon realized that he had entered an extraordinary, almost magical domain. Working out of a small army base that in earlier years had housed North Vietnamese troops, MacKinnon and a team of Vietnamese researchers set out in May 1992 on an expedition sponsored by the World Wildlife Fund. Their mission: to survey the animals in a mysterious area of moist, dense forest largely unexplored by scientists.
Returning from his first hike in the forest, MacKinnon encountered zoologist Do Tuoc, who...