During a fishing trip, detective Vašátko and his friend, painter Horác, casually track down the murderer of a young hitchhiker.

Captain Vašátko of the criminal police and Horác, a painter, bohemian, and amateur detective, escape the stresses of life by going to the river to fish. Horác befriends a young neighbor who is found dead one day. Everything points to suicide, but Horác is still suspicious, so he embarks on an investigation, even resorting to unacceptable tricks that ultimately land him in a very unpleasant situation. Fortunately, his friend Commissioner Vašátko intervenes, understanding his friend's extravagance...

Commissioner Vašátko meets painter Horác while on vacation at a mountain cabin. A diverse group of guests has gathered here, ruled over by the aggressive and arrogant director Skorkovský, who humiliates and abuses his son with nonsensical orders. Horác takes this very badly, as do the others—but they are somehow indebted to the director. The tension in the cottage gradually increases, and the director is found dead. The police cannot get to the cottage because of a storm, so the experienced Commissioner Vašátko takes charge of the investigation. The cottage is full of people who have strong motives for murder...

Captain Vašátko of the criminal police and Horác, a painter, bohemian, and amateur detective, are searching for the murderer of Daniela Jásková, an emancipated young woman who excelled at her job and also excelled at changing lovers. When she is found strangled in her apartment, Vašátko's team begins an investigation. They also focus on the victim's sister, Alena Kášová, who did not like Daniela very much and resented her ability to win over every man. Suspicion also falls on Alena's ex-husband, the sculptor Káš, whom Horác has known since his studies at the academy.

This time, Captain Vašátko of the criminal police and Horác, a painter, bohemian, and amateur detective, will be searching for the murderer of the author of so-called computer poems. Kristián Vích is a mathematician approaching forty. He is very popular among his colleagues. He is secretly dating Tereza, the wife of his rude colleague. The lovers are planning Tereza's divorce and a life together. However, Vích's despotic mother has other plans for her son and a favorite among her colleagues. One day, Kristián's body is found floating in the river, and the perpetrator is, of course, unknown...

Horace was a guest at the home of his old friend Zdeněk, who lived in a secluded house on the shore of a lake with his current wife and his ex-wife. During his visit, Horace witnesses two strange deaths. However, not wanting to get involved in any more cases, he leaves the beautiful place without forming a clear opinion about the events. Two years later, however, circumstances cause him to doubt whether he did the right thing, so he goes to see Vašátko to get some clarity on the case. They both come to the conclusion that a murder took place in Zdeněk's home and also identify the perpetrator. All that remains is to convict him...

Drug dealer Šárlí ended up with a knife in his liver during a drunken brawl as a group of teenagers left a pub late at night. Commissioner Vašátko, who is already enjoying his retirement, is drawn into the investigation by the young man's grandmother, Forejtová, an old acquaintance of his late wife. It turns out that Vašátko's friend, the painter Horác, knows another member of the group, 16-year-old Zbyněk, whom he taught painting some time ago. Zbyněk is struggling with his authoritarian and precise father, the businessman Bouzek, and is clearly hiding something. Vašátko and Horác eventually uncover the background to the murder and its perpetrator. But first, they have to understand the titular "bug," as Vašátko calls the detail that doesn't fit in a criminal case. If the detail is not clarified, the case cannot be closed. In this story, the "bug" is a shoe found at the scene of the crime that does not belong to any of the participants in the altercation.

Captain Vašátko has died. Standing over his coffin in a small rural cemetery, Horác recalls their first case together. They met ten years ago at a country guesthouse, where Horace had come at the invitation of his former college friend Štěpán Novák. Novák had gathered his former classmates from the academy at Mr. Šimáček's guesthouse, where he regularly stayed. It had been 25 years since graduation. Of the five classmates, three remained: one had died, another had emigrated to the US.