In the Enemy's Den (1964)

Russia, 1919. A young soldier of the First Cavalry Army, Aleksei Mikhalyov, is sent to work in the provincial Cheka. Here in the south of the country there is a large White Guard underground led by the elusive Markov. Aleksei gets into the gang, where he is mistaken for his own. The day of the operation to eliminate the white underground is appointed. But unforeseen circumstances destroy the plans of the Chekists.