Inspector Cassin, a renowned Paris detective, departs to the country for a much-needed break. There he falls in love with the innkeeper’s daughter, Nanette, who is already betrothed to a local farmer. On the evening of their engagement party, Nanette and the farmer both disappear. Cassin takes up the case immediately to discover what happened to them and who is responsible.

Early in World War II, Chungking schoolteacher Lin Yang is recruited to help with the dangerous mission of protecting the Allied supply line from Burma into China. In spite of the danger involved, her determination to help is strengthened when one of her young students is killed in a Japanese air raid. Some time later, she is part of a group of Allied representatives departing from Lashio, on a bus traveling the Burma Road back to China. A bridge outage forces them to spend the night in a monastery along the way, and during the night they watch in horror as a supply convoy of trucks is bombed by Japanese planes. The timing and accuracy of the raid brings them to realize that either one of their group, or perhaps the priest in the monastery, is really an enemy agent.