A narrator in Peking recounts how the mysterious death of a distinguished scholar launches an investigation and a perilous expedition across China. Encounters in Shanghai and an opium den lead to alliances, including Stephen Poyning, and a mission that carries them to the obscure town of Kiai, through storms and mountain crossings, and into a concealed valley inhabited by immense birds and a hidden people. A woman of mystery and a hall of wandering souls figure in gradual revelations about the valley's secrets, culminating in disaster, suspenseful escapes, and a final epilogue that closes the narrator's account.