"Poltergeist Mansion Murder Case" is the fifth case arc in the "The (37-year-old) Kindaichi Case Files" spin-off series of The Kindaichi Case Files.
Kindaichi, with Marin in tow, meets two sales representatives in a large PR company over a resort hotel monitoring subcontract, and the four of them, together with several participants who have been selected for the program, enter an abandoned European-style mansion deep within a camp ground for a tour. What follows is a serial murder case that has a connection to this old mansion itself.
Tropes include:
- Accidental Murder: The last of the intended murder targets claims the "two people have a fight near stairs and one of them falls to their death" scenario as to how the culprit's younger sister died. The culprit, however, doesn't buy it, having already gained full knowledge of the incident itself. As the journalist informs Kindaichi and Marin after the case is wrapped up, the culprit is right: The disappeared young girl did fall down stairs, but those people who would later become intended murder targets actually pushed her down the stairs in an attempt to kill her, as well as sealing her Inside a Wall, meaning that the death of the disappeared girl was an INTENTIONAL murder instead of an accidental one.
- But Not Too Foreign: The CEO of the large PR company, according to the staff within said company, is half-Scottish. He appears in person after the murder case is wrapped up and turns out to look distinctively European while having a Japanese name with an English middle name mixed in.
- Damned by Faint Praise: Shortly after meeting the two sales representatives — one female with a male assistant — in the large PR company over the program, the female representative suddenly springs the question about the project on Kindaichi, stating that she had already sent a copy via e-mail to Kindaichi and, therefore, presumed he had read the contents already. Kindaichi hasn't read it, but Marin has, and she promptly answers the question in thorough details. The representative's reaction, however, is "That's a good explanation" with a barely impressed tone, much to Marin's thinly-veiled indignation.
- Exact Words: A lighthearted example. Soon after Fumi wakes Hajime up with a book, their discussion quickly turns to Fumi working as a mystery novelist. Kindaichi expresses his hope that she isn't using her clients' cases as source materials, and Fumi agrees with him... before stating that her source materials are all the cases Hajime himself solved back when he was an Ordinary High-School Student, though she also says that she makes sure to modify details to prevent others from finding out his involvements easily.
- Four Is Death: There were four people — two males and two females — who were directly responsible for the death and disappearance of a college-age student.
- He Knows Too Much: "She" in this case. As the backstory goes, which the journalist among the guests informs Kindaichi and Marin after the murder case concludes, the disappeared girl was targeted for having stumbled upon a drug-addled sex party a group of four people were indulging themselves with while they were inside the abandoned mansion, and they resorted to having her murdered to prevent their act of debauchery from getting out.
- Imagine Spot: Later in the night after the first victim has died, Kindaichi and Marin have a moment alone while the sales representatives escort the guests to their rooms. Marin states at one point about being rather afraid of sleeping alone in light of someone in their group dying, which prompts Kindaichi to imagine her asking to sleep alongside him for a brief second before he shakes it out of his own mind.Kindaichi: No! No! That's on her!
Marin: Manager? What are you talking about? - Inside a Wall: The group of four people plastered a wall with the culprit's sister inside due to her inopportune witnessing of their illicit drug use in their sex party, with her dying within the wall in question. Her deceased body has remained there right up to the present day.
- Intrepid Reporter: One of the participants is a journalist who specializes in the occult. He signed up for this tour in part for the hope of finding out more about the disappearance of a college-age student, which happened seven years ago.
- Jump Scare: Played for Laughs. After two people have fallen victim in this murder case arc, Kindaichi tries to freshen himself up as a result of getting no sleep due to trying to keep things in order all night, before Marin's sudden appearance behind him makes him jump.
- The Killer Becomes the Killed: The group of four people who had actively attacked the disappeared girl before sealing her inside a wall they had plastered shut seven years ago became the intended serial murder targets in the present-day case arc, with three of them falling victim as the culprit intends. The culprit would have killed the last intended target as well, had the culprit not been stopped by some seemingly supernatural force in time.
- Maybe Magic, Maybe Mundane:
- As the culprit states in the confession, the disappeared girl's memories of what happened in her dying moment (namely, being sealed inside a wall a group of four plastered her within) came flooding into the culprit's mind the moment the culprit touched the wall where she has been confined.
- Right when the culprit is about to kill the last of the intended targets, the culprit is stopped involuntarily by one's own body, before the face and the sound briefly change into a different person's — presumably the deceased girl's, as she addresses the culprit in familial terms while pleading for the culprit to stop the murder spree.
- After talking about what they've learned regarding the complete details regarding the serial murder case and its backstory, the conversation the occult journalist has with Kindaichi and Marin centers around the occult and the supernatural.Journalist: Do you know the etymology of the word "occult", Mr. Kindaichi?... It's Latin. It means "hidden things". It cannot be seen, and cannot be touched... There are actually a lot of such "hidden things" out there. Even if not all of them are true, not all of them are lies, either. Why can't there be a few mysterious things out there? *wink* Right?
- Most Writers Are Writers: The conversation between Hajime and Fumi at the end of the case arc establishes Fumi's occupation as a mystery novelist.
- Police Are Useless: As the culprit confesses, the college-age student who disappeared was the culprit's younger sister. Due to the lack of leads, the police eventually gave up on the search effort, and it was by chance that the culprit managed to reach the place where the girl disappeared. The culprit has also decided to personally kill the ones who were responsible for her death, as physical proofs of her being a murder victim were scant at best, even if the culprit is actually aware of the whole truth behind her death.Culprit: Do you get it now, Mr. Kindaichi? This is why I didn't report it to the police. Even if the horrible things these bastards did are indeed the truth, dreams cannot be considered as proof. They will keep on lying as if it was nothing, like she [the last of the people who killed the disappeared girl] just did! They will try to lighten the feeling of guilt! That's why... I had to do it myself!
- Sequel Hook: The case arc ends with Fumi telling Hajime that one of her mystery novels has been nominated as an honorable mention for the upcoming mystery novel award ceremony.
- The Straight and Arrow Path: The first victim is done in by an arrow that gets lodged into the side of his neck. While the wound is not deep, the arrow itself is poisonous, so the target is dead soon after the arrow pierces his skin regardless of where it enters his body.
- Throw the Book at Them: Played for Laughs. On the day after the case arc concludes, Fumi, while making a visit to Kindaichi one day, tries to wake Hajime up by calling him repeatedly. When that doesn't work, she smacks him on the head with a book to make him wake up.Fumi: What time do you think it is?
- Write What You Know: In-Universe. As the conversation between Hajime and Fumi establishes, the ideas behind the materials Fumi uses for writing her mystery novels as an adult are from cases Kindaichi himself solved during his high school years, though Fumi herself tries to hide his real identity and involvement by modifying details in her works.
