The snow leopard is one of the most elusive cats in the world. As few as 3,500 of them may still roam the harsh, forbidding mountains of Central Asia. No one knows for sure.

In 1999 my editor at National Geographic Magazine circulated an email asking for ideas on our "dream assignment". I remembered how my life had been touched when years before I had read George Schaller's "Stones of Silence" and Peter Matthiessen's "The Snow...