Investigation in Psycho-Sleuth is a two-layer system: a scan that tells you what is there, and a debate that tells you what it means. Getting the first layer right is what makes the second layer possible.
Pressing Tab runs a Perception Scan over the scene. The rule is simple and absolute: highlighted objects are real clues, and greyed-out objects are scenery. Anything dim is decoration; anything lit is evidence the game is willing to act on.
This is a mercy disguised as a mechanic. In a deduction game where wrong evidence costs HP, a rule that cleanly separates evidence from background is what makes the debate phase a test of reasoning rather than a test of pixel-hunting. It also means that when a disorder hides part of the screen, what you lose is real — you lose the ability to scan for yourself.
Chapter 1, 「開幕：理之獻祭」 (Overture: The Rational Sacrifice), is the tutorial and the argument is contained. Each character gets two rounds of dialogue. The scene splits into two spatial situations — a ventilation duct and a close-quarters confrontation — and then the debate runs for four rounds, ending in an event called 認知干擾 (cognitive interference). Afterwards, a choice between reporting the incident and verifying it branches into a side CG. Completing the chapter unlocks the 大廳檔案庫 (Hall Archive).
Chapter 2, 「扭曲證詞」 (Distorted Testimony), is built on memory fragments that restore testimony the cult tampered with. The contagion adds symptoms and therefore dialogue, and a clue on the hall bulletin board opens the chapter's second half. The debate runs four more rounds and ends in memory rewriting. Three failures trigger the 集體誤判 (collective misjudgement) bad ending. The chapter ends on a choice to publish your findings or keep them private to your sister, and completes by unlocking the 病能百科 (Madness Encyclopedia).