In the village of Momchilovo, located at the very foot of Karabair, an unheard-of crime was committed - at night someone climbed through a window into the premises of a military-geological point, stole a secret diagram and two thousand leva, while seriously wounding police sergeant Stoyan, who was guarding this extremely important object. That same night and the day before, not far from Momchilov, active operation of an ultra-short wave radio station was noticed, which exchanged coded messages with the same station on the other side of the border. Suspicion falls on the young Momchilovo teacher Methodius Parashkev. Literally a minute before the attack on Stoyan, he passed by a military-geological point. The evidence against him is so convincing that there is almost no doubt about his guilt. Only one of the Bulgarian counterintelligence aces, Avvakum Zakhov, is not at all sure that the criminal is Parashkev. The state security captain believes that the teacher was framed.