Komisario Palmun erehdys
Tags: insanity, murder

Plot synopsis:
The film opens with a scene of guests arriving at the crime-themed dinner party of Bruno Rygseck, the rich and decadent heir of the Rykämö concern. The guests are his cousins Airi and Aimo Rykämö, Airi's fiancé Erik Vaara, who works for the concern and strongly dislikes Bruno, and Irma Vanne, the daughter of vuorineuvos Vanne. In order to scare them as they arrive, Bruno has dressed up as the Grim Reaper.
The next morning, inspector Palmu and detectives Virta and Kokki are informed that Bruno has drowned in his indoor swimming pool after slipping on a bar of soap. They head to the Rygseck house to conduct a routine investigation. The party guests (with the exception of Vanne), as well as Bruno's aunt Amalia Rygseck and his estranged wife Alli Rygseck, are present at the house, as all of them had had something to discuss with Bruno that morning. As Palmu inspects the bathroom, he begins to suspect that Bruno was in fact murdered. When the policemen are shown around the house by Bruno's manservant, Veijonen, they find Vanne and famous author K.V. Laihonen engrossed in lively conversation in the basement. They are oblivious to the morning's events, as they had entered the house through the back door when coke was delivered in the early morning and have since been in the basement. Although Laihonen does not know Bruno or Vanne from before, he had been invited to the house by her to get back the stolen manuscript of his unpublished novel.
The atmosphere in the house becomes increasingly hostile towards the investigation as Palmu asks more detailed questions about the morning's events. He learns that the previous night, Aimo had stolen Amalia's cat and brought it with him to the dinner party, where Bruno had poisoned it and invited her to view the cadaver for his amusement. Despite Palmu's suspicions, the investigation is closed due to pressure from the powerful Rygsecks and because there is no evidence to prove that the death was not accidental. Laihonen asks the policemen and Vanne to join him at the luxurious Hotel Kämp for a late lunch.
At Kämp, Vanne tells the policemen more about the previous night. They had been playing a game in which each contestant has to commit a crime that the victim cannot report to the police. The winner was to be chosen by Vaara at the party. Her crime had been to steal the manuscript; Aimo's to steal the cat; and Airi's to have ten of Aimo's promissory notes signed by Bruno. She had refused to reveal how she had gotten them, other than that it was blackmail. Bruno had then asked Vaara to come to his bedroom in order to show him his crime in private. Afterwards, Vaara had stormed out of the house in fury, after stating that Bruno had won the contest.
When Palmu and the detectives arrive back at the police station late in the afternoon, they are told that Alli Rygseck has been poisoned with prussic acid mixed in her absinthe. She had been back at the Rygseck house to discuss with the family members who was to inherit from Bruno: she had insisted that she should get the house. Bruno's case is now also re-opened, and the policemen head back to the house. Palmu interrogates Airi about the promissory notes, and she reveals that Aimo had been forging Bruno's signature to pay off his gambling debts. Bruno had told her that he would contact the police about it unless she were to agree to do something, although she refuses to specify exactly what. In Bruno's bedroom, Palmu finds an album of nude photographs he had taken of his female friends, with one page torn off.
That evening, the policemen meet Bruno's uncle Gunnar Rygseck, the head of the Rykämö concern, at his office. He tries to bribe Palmu and claims that Bruno was suicidal and had intended the poisoned absinthe for himself before dying accidentally. Next, Palmu confronts Vaara, whose office is in the same building, about what Bruno showed him. It is revealed to have been a nude photograph of Airi, which Palmu notices is a forgery. He tells Vaara that Aimo killed Bruno and that Airi will be imprisoned as an accomplice as she has tried to protect her brother: this leads Vaara to confess to Bruno's murder. Palmu asks for Airi, who also works for the concern, to come to Vaara's office. She confirms that the photograph is forged, and finds the idea that her brother killed Bruno laughable. Vaara takes back his confession, and Palmu admits that he never truly believed either him or Aimo to be the murderer.
Palmu calls the Rygseck house, where Amalia is moving in, and is told by her that Veijonen has disappeared. Palmu goes to interrogate Vanne again, and she confesses to have in fact secretly stayed in Alli Rygseck's old bedroom on the night of the party. When she walked through the corridor leading to the bathroom the next morning in order to get to the back door, she thought that a stair creaked behind her, as if someone else was there as well. Palmu places her on house arrest at Laihonen's apartment.
In order to get the murderer to act, Palmu sends detective Virta to tell all the suspects that Vanne knows something about the murders. He is also to get Bruno's photo album from the Rygseck house and to go show it to Vanne. At the house, Amalia convinces Virta to give her his gun for protection as she is scared of Veijonen. When Virta returns to the station, he learns that Veijonen has been caught and is cleared of the murders. Soon after, Palmu calls Laihonen and asks to speak to Vanne. He admits that she has gone to help Amalia search the house – he had lied to the gullible Virta earlier that she was asleep. The police rush back to the Rygseck house, and stop Amalia from shooting Vanne. In the struggle, Virta is shot in the shoulder.
In the final scene, it is revealed that Amalia has been mentally ill for some time and that she murdered Bruno as revenge for killing her cat. The murder weapon was her umbrella with a sturdy wooden handle that she always carried with her. As she is elderly and not of sound mind, she is not prosecuted but is left to the care of her brother.