In the last days of 1933, Belgrade is shocked by a gruesome murder at Mt. Avala, in the medieval fortress Žrnov, where the Monument to the Unknown Hero is planned to be erected. Inspector Stanko Pletikosić and his assistant Zečević take over the investigation. After the arrest of “crazy Rajko”, an order comes from the top of the government to stop any further investigation. Stanko is suspicious about that theory and seeks help from his former colleague and boss, Tane Tankosić.

Count Novicki, Prince Pavle, banker’s daughter Maja Davidović, secret agent Mustafa Golubić, are some of the co-conspirators in the assassination of King Alexander, but all of them acting in their own interests. The trail of the killer leads to Mt. Avala, but just as Stanko thinks that he has uncovered an important clue, a new murder takes place.

The planning of the assassination of King Alexander, opium trafficking, Macedonian terrorists, Jatagan mala, the mysterious Thule Society, Marija Oršić spinning her web, are just some of the stories leading to the final shootout and the solving of the Belgrade murders. Tane and Stanko realize who is organizing the assassination of the king, and the deception that leads them back to Žrnov.