"The Twin Murder Incident" (aka "1/2 Murderer Case") is the fourth story in the Short File Series of The Kindaichi Case Files.
In this murder case, it's suspected that a wealthy man is killed by one of his daughters. While the victim has in his mouth some hair from his killer, his daughters are identical twins, so Kindaichi is enlisted to determine which of his daughters is the culprit.
Tropes include:
- Continuity Nod: Miyuki briefly mentions the treasure isle murder case to Saki, as Kaya marked her debut appearance there, throughout which Saki had no involvement, and hasn't appeared in any of the cases that involve(d) him.
- Exact Words: Played for Laughs. Kaya (an undercover cop from the Treasure Isle Case arc) requests Kindaichi's help to solve the murder, promising that she'll let him see the inside of her mysterious box if he consents. Kindaichi agrees, only to find at the end of the chapter that inside Kaya's box is... another box. Kindaichi isn't pleased with how it turns out.Kaya: I said you could open the box, but I never said you could take a look at what was inside.Kindaichi: How... How can you use such a childish trick...?!
- Luke, I Am Your Father: The man who was murdered by one of the twin sisters turns out to be their biological father, not merely a stepfather like they had believed. The revelation is relayed by the man's fiancee, who learned of the news from the man while he was still alive.
- Polar Opposite Twins: The twin sisters in this case are actually opposite of each other personality-wise. One is reserved and quiet, whereas the other is outgoing and talkative.
- The Unreveal: Kaya coaxes Kindaichi into helping her to solve the murder case under the promise that she'll let him see the inside of her mysterious box if he agrees to it. Kindaichi agrees, only to find at the end of the chapter that inside Kaya's box is... another box, much to Kindaichi's chagrin.
- Self-Made Orphan: The victim in this case was killed by one of his daughters. A slight twist comes in that his daughters had no idea the man was their biological father until the man's fiancee tells them near the case's end.
- Why Did It Have to Be Snakes?: It turns out that one of the twin sisters has acrophobia. Kindaichi concludes that, between the twin sisters, the acrophobic one is the culprit after examining the crime scene, which is a fire escape staircase between the 25th floor and the 26th one, with a clear view to the outside, only a handrail for support, and no protection from the wind.
