What had been a calm encounter with Inami Nahoshi takes a turn when Hondomachi outs her as the Gravedigger mastermind. Nahoshi is calm because her accomplice Kazuta is in the house with all the kitchen knives.
A dust-up ensures, with Matsuoka receiving a flesh wound to the shoulder and Hondomachi stabbing Kazuta to death, much to Nahoshi’s uncharacteristic dismay. These two detectives are just powerful electromagnets for trouble.
Demonstrating that the detectives at the Wellside are always working, five of them spend their time a police officer’s funeral discussing the Walker case. Why does he keep showing up in the id wells of serial killers, and in the same whimsical form? The name of the inventor of the Mizuhanome, Shirakoma Nishio, comes up, which is sure to be important later on.
While this case are already complicated enough, one of them brings up the possibility one of them is a mole working from within. Considering we only have cursory familiarity with these five detectives, the eventual reveal of one of them as Walker wouldn’t be that narratively satisfying, at least not yet.
Using the cognition particles from Kazuta’s urge to kill (which manifested in a dying kiss to Hondomachi), Narihisago is injected from the flying house to a train. On it, Kaeru is (obviously) dead via stabbing. When he follows the very obvious bloody footprints, he discovers the train is a closed loop, ending right back where it begins.
The Wellsiders determine this is the very train Nahoshi’s mother jumped in front of…while Nahoshi was on it. A high school-aged Nahoshi is here to, with a younger Kazuta sitting on the opposite side of the aisle. There was once a time when Nahoshi abhored seeing dead things or people; her mother’s suicide flipped that sensibility.
IRL, Nahoshi reveals all the locations of the barrels containing her victims, but on the id train she didn’t kill Kaeru; Kaeru killed herself. When Narihisago comes to this conclusion, he weeps in her lap. He grows weary of coming upon her corpse over and over again. He wants to save her, but like the train, he’s going in circles. One wonders how long he can keep up the Brilliant Detective act with his sanity intact (such as it is already).
That brings us to Hondomachi, the other protagonist. Matsuoka recommends her to be a second Brilliant Detective utilizing the Mizuhanome. Hondomachi is flattered, but Matsuoka considers it a practical decision, in part to protect him and their colleagues. Hondomachi has killed more than once—by attempting to kill herself and then killing Kazuta. Matsuoka laments he couldn’t keep her out of this business, but she’s too suited for it, and there’s no turning back.
The Wellsiders make a connection between the surveillance devices found in the Perforator’s house match those used in the case involving the “Challenger”, AKA Katsuyama Denshin, the man who killed Narihisago’s daughter. With every subsequent case, ID:INVADED adds another piece to the larger puzzle of John Walker and the root of Narihisago’s fall, just as his possible successor begins her ascent.