In Maribor, the final preparations are underway for a congress on the topic of ecology, organized by the ambitious director of the institute, Ema Znidarsic. A special guest is Peter Divjak, an internationally renowned expert who has been lecturing in the USA for years. Although the beginning of the meeting of the congressmen was idyllic - under the leadership of Ema's colleague Marta Jenko, they went on a trip to Pohorje - but on the morning of the big event, the body of the main star of the congress, Professor Divjak, washes up on the Drava river. The signs show that Divjak died a violent death, so Inspector Martin Vrenko and his new colleague Tadej Krajnec set out to find the perpetrator.

A woman walking her dog finds a stabbed waiter in front of an inn. It turns out that on the night of the murder, congressmen dined at the inn. Repeated debriefings with congressmen yield no clues as to who might have done the killing. Inspector Vrenko finds himself in front of a puzzle that he cannot solve. His father Boris causes additional worries, because he has an accident and ends up in the hospital, so that now he will have to take care of him as well.

Inspector Vrenko and his father Boris go on vacation to the famous Prekmurje spa, where he comes to the aid of his colleague inspector Štefan Houra. A murder has taken place in a prominent Prekmurje hotel family, the victim is the owner of the hotel, and every trace of her husband is lost. Although Inspector Houra would like to close the case as soon as possible, as he is convinced that it is a "classic Slovenian tragedy" after a marital dispute, Vrenko's eye notices details that take him all the way to Maribor. While Vrenko solves the murder with Houra, father Boris befriends Ana, a voluntary peer, in the thermal baths.

Inspector Vrenko and Štefan Houra also track down drug smugglers while searching for the killer. All traces lead to one of the guests of the Ajdov guesthouse, Jimi Kos, but the problem is that Jimi Kos does not exist in the official records. Vrenko's pursuit of the possible motives of the perpetrators brings him back to the scene of the hotel owner's murder, where he stumbles upon a trail that leads him across a whole constellation of Prekmurje characters to the real perpetrator.

While walking in the forest, a hunter comes across a decomposed corpse. It turns out that he is the son of a well-known Svecina winemaker, whose disappearance was not reported by anyone. Given the fact that the murdered man has recently taken over the family business, a whole series of suspects opens up for Inspector Vrenko, from the victim's close relatives to colleagues, but they all have one thing in common - an unusual obsession.

It turns out that former close associates Alfi Filipcic and Aleksander Pucko have unfinished business, as Aleksander reacts violently to Alfi's visit. Aleksandr's children Bojan and Iris also knew about the irregularities committed by Filipcic in the company, so they fired him. However, they did not know everything about their father. Vrenko finally obtains a warrant to investigate the weekend, but too late, as the weekend is thoroughly cleaned, and it is also too late for another life that ends at the other end of Maribor, which again fills Inspector Vrenko with melancholy. He knows that evil must be fought, but he finds it difficult to accept that it cannot be completely eradicated.