A scientific expedition remains in the taiga for the winter. Encrypted materials of vital defense significance are being sent with engineer Sapov, accompanied by former partisan Oloni, who is to board the engineer on a plane. At one of the stops, Inspector Petrov unexpectedly appears to Sapov. Petrov, in reality a former White Guard named Yanyga, is currently serving in Japanese intelligence. The saboteur's goal is to steal the secret documents and flee abroad on the plane...
