Joanna Greenfield dreamed of traveling to East Africa to study one of the last known populations of wild chimpanzees. When she was offered a once-in-a-lifetime chance, the young student set off from peaceful Kenya into politically hazardous Uganda. From there, a small team of guides led her into the mountains.

In stunningly evocative language, Greenfield depicts the beauty of the rainforest and the determination required to wait for one transcendent encounter in the wild. But even one of the most remote places in the world is not immune to terrifying man-made conflict. Greenfield and her...