Richard Pokora is a talented young scientist who won a prestigious award as a student. He therefore has the opportunity to continue working on his scientific discoveries in an important research center in Paris. He experiences contradictory moments there - he can collaborate with the greatest expert on the same problem, the genetic influence of agricultural crops, but at the same time he experiences loneliness hard. Only his only childhood friend tries to distract his thoughts. In her spare time, Pokora goes to Notre Dame and writes her diary. Even directly in French to practice the language. His life and especially his work are disturbed by anonymous threats, which he already received in Prague, but it continues in Paris. He doesn't pay too much attention to it, trying to focus on research. A few months later, when they are at the end of their research, tragedy strikes. Professor Calbot is murdered and perishes at the hands of both the assassin and Pokor on the same day. It turns out that the death was caused by an unknown highly poisonous substance originating from the Amazon. A complex search for the killer begins, which will have to be searched not only in Paris, but also in Prague. And so the Parisian criminal investigators from Zlatníký embankment, Commissioner Morelon and Inspector Maigret appear on the scene, as well as the criminal council Hladík and his murder squad in Prague. It turns out how difficult it is to find a killer who is a fanatical supporter of his perverted idea.