MY DEAR KILLER

Police Commissioner Luca Peretti is assigned to investigate a seemingly isolated murder case. Umberto Paradisi, a private investigator for an insurance company, had been decapitated by an excavator at a rural swamp area. Soon after, the worker who operated the excavator is found hanged. Peretti discovers a clue at the scene indicating the driver of the excavator did not commit suicide, but was in fact murdered. He also discovers that the murdered investigator was working on a cold case involving the kidnapping and murder of Stefania Moroni, the young daughter of a wealthy industrialist; when her father attempted to pay the ransom, he too was kidnapped, and both of them were left to die. The investigator had evidently discovered a lead, and was trying to sell the information to the victims' relatives.

Peretti proceeds to question other people connected with the Moroni case, including Stefania's traumatized mother, her uncle Oliviero—who lost one of his hands during the war—along with his wife, other relatives, and the family's servants. However, additional murders begin to occur. The investigator's wife is strangled to death at a public transport station, Stefania's kindergarten teacher is mutilated with a circular saw, and Mattia, a destitute man who lived in a small shack near the site of the investigator's murder, is bludgeoned to death with a statue.

Arriving at the shack where Stefania and her father were left to die, Peretti realizes that Stefania had left a clue to her kidnapper's identity before dying, evidently on the back of a mirror. That night, the murderer tries to kill an elderly lady who unknowingly came into possession of the mirror, but Peretti arrives at the scene just in time, forcing him to flee. Upon recovering the mirror, Peretti examines the back of it and realizes that it perfectly implicates the killer.

Peretti summons the police to the Moroni family home, and with the entire family present, proceeds to excoriate the killer for killing in cold blood while overlooking the one detail that revealed his identity. Peretti then produces the mirror, and upon showing the back of it to Beniamino, he screams before someone cuts off the lights in the room. Once the chaos settles and the lights are turned back on, Oliviero is found sobbing in the corner behind a chair. He admits to having killed Stefania and her father out of jealousy for the latter's wealth, and all the others in an attempt to cover his tracks.

Peretti orders the police to arrest Oliviero as the camera focuses on the back of the mirror, revealing the clue to the killer's identity—a human figure, drawn by Stefania, missing one of its hands.

Inspector Peretti gathers the Moroni family and presents the mirror clue, leading Oliviero to confess to the murders out of jealousy and greed. He is arrested as the camera reveals Stefania's drawing identifying the killer.

The ending ties the murders to family betrayal and greed, with the child victim’s final act bringing justice from beyond the grave. Peretti’s methodical approach and reliance on overlooked clues underscore the film’s emphasis on thorough police work and the tragic cost of familial corruption. The reveal is as much about psychological closure as criminal justice, staying true to the giallo tradition of unmasking the killer in a dramatic family showdown.