When we meet the self-described “brilliant detective” Sakaido, he’s literally gone to pieces, as has the entire world around him. He soon calms down from the initial horror of such a status and puts himself back together, save a few gaps in his arm. He learns those are a boon, which allow him to fit the various pieces of his environment back together.
We’re in the same boat as Sakaido: a pile of pieces are spread out before us instead of a “whole” world. But it’s not really a world; it’s the unconscious of a serial killer Sakaido is investigating, and all of his victims (plus one little girl) dwell within that unconscious.
As we pull out to the real world, we see a team cops hard at work on the outside of the “Id Well” created by the Mizuhanome system led by Momoki, while Sakaido works within it. There are clues within the well for those clever enough to see them, and Sakaido is the man for the job. We also learn that only someone who has killed can enter such wells.
Once Sakaido finds enough clues as to the murderer’s whereabouts (literally piecing the world back together), field analysts Matsuoka and Hondomachi (a grizzled veteran and green rookie, respectively) head out to track him down. But their quarry, known as the “Perforator” due to his M.O. of drilling holes in his victims’ heads, uses his latest victim as a decoy to misdirect Matsuoka, then kidnaps Hondomachi.
When the Perforator threatens to drill a hole in her head, a defiant Hondomachi realizes the only way she’ll be located by her colleagues is to drill the hole herself, so she drives her head into the spinning bit, creating an Id Well of her own into which Sakaido is quickly transferred. It’s a reckless risk, to be sure, but it shows us that Hondomachi is willing to take those risks for the sake of Justice.
Unlike the puzzle world of the killer, Hondomachi’s well is a wasteland filled with mammoth drills, one of which kills Sakaido (or rather his avatar within the well) within 69 seconds. But that’s enough for HQ to determine Hondomachi’s whereabouts, and Matsuoka manages to rescue her and arrest the Perferator, who is so impressed by Hondomachi’s initiative he surrenders willingly.
But the Perferator is only a symptom. The disease this weird futuristic police force is pursuing is known as “John Walker”, who resembles the guy on the whisky bottle. His avatar appeared in the Perforator’s Id Well, and is believed to be the one turning people into serial killers.
Sakaido is extracted from the Id Well and escorted back to his spartan prison cell, decorated only by dozens of photos of his wife and daughter Muku—a very effective way to wordlessly humanize him. Every Id Well he’s dove into has featured a murdered girl in Kaeru, who may not look like Muku but still reminds him of her, and why he’s in this strange business in the first place (I’m sure we’ll learn the details of that later).
While there’s a bit of a learning curve with all of the jargon, and there are more than a few similarities to PSYCHO-PASS, the third season of which I didn’t bother with, ID:INVADED nevertheless scratches a future crime unit itch I wasn’t aware of until now.