In the forest near the village of Drahovice, a nurse from the local health center is found murdered. Three months ago, another young woman died nearby and a sexual motive was proved in the case of her murder. In the case of the nurse, the motives are not so clear. Two criminologists from Prague - Major Kalas (Rudolf Hrusínský) and Lieutenant Varga (Radoslav Brzobohatý) - patiently collect all available leads and question the villagers.

A car deliberately runs down a young man on a road by a small border town. The locals recognize the dead man as one of the students who were there on volunteer work some time before. The police detectives, Major Kalas (Rudolf Hrusínský) and Lieutenant Varga (Radoslav Brzobohatý) can then get on the trail of the people with whom the victim was involved, especially at the photographic studio headed by Bohuslav Pacer (Bohus Záhorský).

An escort composed of three people transports a huge amount of new one-hundred crown banknotes in a special railway car. At the 196th kilometer, a village girl is waiting at the railway crossing and spots two men removing some packages from the track. The scene is immediately followed by the report of a gun and the unwanted witness is shot dead. Soon afterwards, on the 201st kilometer, the train explodes. Only one of the escorts Lenk (Radoslav Brzobohatý) survives the explosion, taken to hospital with serious injuries. Criminologist Major Kalas (Jirí Sovák) and the very young Second Lieutenant Karlícek (Jaromír Hanzlík) patiently gather facts, leads and testimonies.

Two seriously injured patients are brought to the hospital at almost the same time: truck driver Honza Linhart, who had an accident, and a young woman found unconscious in a forest by a man picking mushrooms. The woman is identified as Katerina Marková, the divorced mother of a young girl. Major Kalas (Rudolf Hrusínský) suspects that she is a victim of mugging since a bloodstained small ax has been found near the site of the crime and, according to witnesses, Ms Marková was missing her watch and a bracelet, from which a gemstone has also been discovered. Linhart has lost his only kidney in the accident; in order to live a normal life again, he will need a kidney transplant from the mugged woman if she dies.

On the Trail of Blood is a crime movie set in Central Europe. It follows the investigation of a serial child killer and the multiple suspects involved. The plot also includes themes of loss, unhappy marriage, and hidden secrets. The movie delves into the dark underbelly of society and explores the complex relationships between the characters.