A foreign spy service sends Mitar Petrović, an engineer, to Belgrade. His mission is to contact an enemy group that for some time has been planning to sabotage a project of great significance to the Yugoslav economy. The enemy action also has a political dimension as it is planned to take place during an international symposium of scientist in Belgrade. Stopping at nothing, Mitar's group prepares the final coup. Gradually the security service uncovers this clever and well-planned plot…