Guides → Optional investigations
All 8 optional investigations
Quick answer: there are eight achievement-linked optional investigations, spread across Chapters 1–4. Complete each one when you reach its area: some locations cannot be revisited after the chapter, and several rewards are permanent weapon or inventory improvements.
Investigation checklist in story order
| Ch. | Investigation | Location | Clue / answer | Reward |
|---|---|---|---|---|
| 1 | The Inheritance | Apartment 5 / Radio Store | Connect To Martin + From A Sister; safe code 1908 | Ammo, healing item and achievement |
| 2 | The Other Gods | Redemption Church | Star Key, Trident, crypt notes and obelisk symbol sequence | Dream Essence and achievement |
| 2 | The Red Press | Printing House | Collect Plates A, B and C; validate all gold or all silver | Shotgun stock or Dream Essence + achievement |
| 2 | The Siren's Call | Devil's Reef Hotel | Safe Code Letter + Baby, One More Tide lyrics; code 2137 | Voss Aiming Grip, ammo and achievement |
| 3 | The Whisperers | Akeley Wireless Room | Three brain testimonies; enter 13, 05, 36 | Dream Essence and achievement |
| 3 | The Vault | Akeley Storage | Collect notes containing 0, 1, 3 and 8; code 1308 | Submachine-gun upgrade and achievement |
| 4 | The Drowned | Fish Market Fishing Shop | Lighthouse, Rings, Star, Squid symbol order | Submachine-gun upgrade and achievement |
| 4 | The Damned | Fish Market Salt Storage | Sixteen Punishments clues; select I, IV, IX, XVI | Grenade-launcher upgrade, Dream Essence and achievement |
How optional investigations work
Finding one note is often not enough. Open the Investigation space and connect the related evidence so the deduction becomes active. A puzzle can sometimes accept its fixed code early, but completing the clue chain supplies the intended context and ensures the investigation achievement is registered.
Optional cases do not gate the main story. They are still worth doing because they award Dream Essence, ammunition, inventory space and weapon attachments that reduce pressure later in the campaign.
Chapter 2 investigations
The church, Printing House and Devil's Reef Hotel contain three separate cases. Do not leave for Akeley Hospital until you have completed the obelisk sequence, chosen a Printing Press reward and opened Room 301's safe. The detailed answers are in the church guide, puzzle list and Room 301 guide.
Chapter 4 Fish Market investigations
The Drowned locker and The Damned Salt Storage door are different puzzles. The locker uses four pictures; Salt Storage uses Roman numerals. Finish both before entering the Broken Hold. For the second answer and its prerequisite route, see the Salt Storage guide.
Missable checklist
- Open the Apartment safe before leaving the flooded residential area.
- Collect all three Printing Plates before moving on from Chapter 2.
- Finish both Akeley investigations before the final hospital escape.
- Finish both Fish Market investigations before the Broken Hold boss route.
- Track E.R.C. Crates separately; they use a different one-run achievement checklist covered in the E.R.C. guide.
Investigation names cross-checked against the launch achievement list; clue groupings and routes compiled from the GameSpew walkthrough and our achievement guide, reviewed August 20, 2026.