Just read through here so I don’t have many ideas yet.
Though I’m interested as to how this serial killer got in. I’ll assume something prevents the serial killer being the sister since someone would’ve surely shot at that already?
As to my actual idea: **the killer is one of the parents (hence foreshadowing) and they are hidden somewhere where they can reach the house that isn’t considered in the house.** An example would be a gate that was locked by the key and the parent is sitting outside; they’re past the reach of the key but not in the house. Many places could be this: they could be in an attic, a conservatory or even inside the wall insulation if we wanted to get stupid.
Though this seems way too complex to be the solution…
Just to cover some bases: The sister was killed in between the point in time when the narrator stated that there was only them and their sister in the house and the sister being murdered, then went to kill the narrator.
The narrator doesn’t consider the serial killer to be a person and thus can state that there are only two people in the house despite the serial killer already being in the house at that time.
While crushing the key may have made it ‘unusable’, and it is impossible to open the house without using the key, it was still possible to ‘use’ it nonetheless as a lockpick! With this, the key becomes unusable but was still usable to open the door.
The thing the narrator knocked off of the table are the remaining parts of the key he crushed. The key fell and slipped underneath the door, and as Karifean said, it could still be used as a lockpick, so the killer picked it up and gained access to the house.
On a more serious note, let’s backtrack a bit to a more feasible thing. The killer broke the lock. This satisfies the red truth about doors never being locked or unlocked but still allows the lock’s barrier to fail.
Hmm, the only thing Picto’s answered with a lime question thus far, is my theory of the narrator being an accomplice… maybe we should all focus more on that.
I thought of that earlier, though I thought it wouldn’t work. I’ll cover a few more bases. The killer broke down the door in order to enter the house, by breaking the lock or kicking it open or by some other means.
Well then, this serial killer was in the house at the beginning of the narration. They have set up some sort of trap that will kill the narrator’s sister. They are standing before the narrator at the beginning of the narration, which is why the narrator is not looking at the headline. The thing that the narrator knocks down is not important to the sister, but important to the serial killer, who is also female. It is a sword, her weapon. When the narrator “knocks it down” it kills the serial killer, which is why at that point there are only two people in the house. His sister then is killed, because the trap was on a timer. The serial killer had been in the same room as her when she set up the trap. The narrator knows she is dead because he hears the trap go off and his sister scream. The narrator dies because he had been stabbed by the killer earlier. The thing he decided to go through with was destroying the key, which prevented him from being saved after being fatally wounded.
Fine. Similar to the narrator, the narrator’s sister was also given a fatal wound but did not die immediately. She had been moaning in pain the whole time, and the narrator knew she had died because the moaning had ceased. The rest of my theory stays the same.