The foreign spy Thomas arrives in Sofia. In order to get his hands on some documents, he decides to use the young man Boyan as his cover. The action takes place at the "Orient Express". A young foreigner-drug addict, the train attendant and the secretary conduct the mission. The train attendant and the drug addict are killed. Boyan is a major suspect. However, Thomas is a very naive man. The Bulgarian counterintelligence discovers the plot.