Abyss Messenger: The Last Five Letters — Complete Walkthrough
Version: the 25 October 2026 rewrite. The old "journalist Lin Xi / ancient leviathan / five parcels" story is gone; the fifth letter and "finish your brother's round" are the new main line. Spoilers: five letters, four questions, twelve echoes, four endings and the hidden 34.2. Where these numbers come from: everything below — the five letters, four questions, twelve echoes and four endings — is what the 25 October 2026 rewrite actually contains, not an estimate. You see them in the game like this: the five letters are the ones handed to you by each recipient (the name shows as you deliver); the four questions are the prompt boxes in Su Qing, Ah Hai, Ming Yue and Dr. K's conversations; the twelve echoes are in the Echoes codex (button bottom-left, shows n/12); the four endings are on the final choice screen. Chinese and English lines match one to one, and the old "three endings" wording is dropped.
The route
The five letters form a chain; you cannot skip one:
Old Chen (Lighthouse & Dock) → Su Qing (Southern Coral Reef) → Ah Hai (The Wreck) → Ming Yue (Bone Shrine) → Dr. K (Abyssal Lab) → the fifth letter → endings
At each stop: talk to the current recipient, take the letter for the next person, walk there, answer one question, then hand it over. The fifth has no recipient; handing it over opens the ending choice.
Controls: WASD to move, Shift to sprint, E to interact, drag to look. Zero oxygen is not an immediate fail: you enter a 45%-speed critical state with ten seconds to find a bubble.
Letter one: Old Chen → Su Qing
Old Chen at the Lighthouse & Dock explains the island isn't breathing: a pump installed in 1978 draws water every four seconds; in 1962 a cable ship went down on the reef and every family signed a secrecy paper; Lin Yu went into the pump station three years ago and Dr. K locked the door.
He gives you Letter One: The Tide Log for Su Qing, and says: "The tide is four seconds now."
Su Qing at the Southern Coral Reef asks:
How many seconds does the pump take now? Not Old Chen's old number.
- Answer: 4 (or four, 4s, 4 seconds).
- Two pieces of support: Old Chen's log goes from six to four; the gauge under the lighthouse also reads four.
- After two misses, the hint points back to "six before, four now."
- On success she gives you Letter Two: The Fluorescence Record for Ah Hai, and says: "Tell him 400 percent."
Letter two: Su Qing → Ah Hai
Ah Hai at The Wreck asks:
Three months ago this patch read 12 units. Su Qing says it rose 400 percent. So what is it now?
- Answer: 60 (or sixty, 60 units). 12 × 5 = 60; 400 percent is the increase, not the final value.
- Two pieces of support: Su Qing's 400 percent increase and Ah Hai's baseline of 12 on the sonar chart; neither works alone.
- On success he gives you Letter Three: The Chronicle Page for Ming Yue, and says: "Tell her 222, not two hundred."
Letter three: Ah Hai → Ming Yue
Ming Yue at the Bone Shrine asks:
What was "two hundred years a cycle" recalculated to? The thirteenth rib will confirm it.
- Answer: 222 (or two hundred twenty two, 222 years).
- Two pieces of support: Ah Hai's chronicle page and the 222 rings on the thirteenth rib.
- On success she gives you Letter Four: The Shrine Rubbing for Dr. K, and says: "Tell him 52.9 hertz."
Letter four: Ming Yue → Dr. K
Dr. K in the Abyssal Lab asks:
What frequency does the pump run at? Ming Yue and my EEG mean the same number.
- Answer: 52.9 (or 52.9hz, 52.9 hertz).
- Two pieces of support: Ming Yue's account and Dr. K's EEG aligning at minute seven.
- On success he gives you Letter Five: For Lin Xi. It has no recipient; handing it over opens the ending choice.
The fifth letter and four choices
The ending screen offers:
- Publish the five letters: the 1962 secrecy paper is removed; the sixteen names and Lin Yu enter the public record. The village loses its tourism lease and the reef is closed.
- Give them to the families and seal the station: five copies go to five families; the beast story continues and the pump is locked again. Lin Yu isn't in any public record, but he has a place at five kitchen tables.
- Hidden entrance: put the fifth letter back into the pump. In the ending-screen input, enter the difference between the two frequencies, 34.2 (not 52.9 or 18.7). You hear Lin Yu's recording: "I locked the door myself. Don't wait for me."
- The choice unlocked by all twelve echoes: send the twelve echoes out with the fifth letter; the pump answers with seventeen names, the last one Lin Yu.
There is no bad ending; the difference is who you are willing to give that night to.
Where the twelve echoes are
Echoes don't change the main branch; walk close to a glimmer to collect them. All twelve add the fourth choice at the ending. In the Echoes codex they're sorted by region, and each has its own picture. They fill in what the main line leaves out and never give puzzle answers.
- Lighthouse & Dock (2): The Six-Second Lead, The Scorched Nameplate.
- Southern Coral Reef (2): Lin Yu's Route Book, The Fish That Stayed.
- The Wreck (2): The Back of the Chronicle, The Later Coin.
- Bone Shrine (2): The Thirteenth Rib, The Caretaker Roll.
- Abyssal Lab (2): Minute Seven on the EEG, Coral of Two Ages.
- Two more (2): The 1978 Hand-Drawn Sonar, To the Next Courier. These two aren't in the five districts above — they sit out on the sea lanes, picked up as you travel between regions, and in the Echoes codex they fall under the "Region" group.
Oxygen and grades
- One tank lasts roughly one sprint through the main line; sprinting saves time, bubbles save oxygen — pick one.
- At zero oxygen you enter critical: 45% speed and ten seconds to find a bubble. If you fail, the current carries you back to the lighthouse, and you keep the letter.
- Each delivery is graded by the ratio to an ideal walk, in four bands: S (Abyssal Sprint), A (Steady Delivery), B (Smooth Arrival), C (Made It). It is an optional challenge; it changes no story or ending.
What the rewrite changed
Before 25 October 2026 the main line was "journalist Lin Xi lands on the island, delivers for five people, uncovers an ancient leviathan." It is now "Lin Xi finishes the five letters her missing brother Lin Yu never delivered." The beast becomes the village's story about a 1978 pump station; the 1962 cable ship and its sixteen names become the real account. The four answers remain 4, 60, 222 and 52.9 (in the second one, 400 percent is the increase; the figure you send is 12 × 5 = 60), but each now needs two pieces of support and one artifact, not a repeated line.
Old saves are incompatible; the title screen starts again from the first letter.
How you can check these numbers yourself
Every quantity above — the five letters, four questions, twelve echoes, four endings, 34.2 — comes from what the live 25 October 2026 build actually shows, not the old guide:
- The five letters: the ones each recipient hands you, with the name shown on delivery.
- The four questions and four endings: the prompt boxes in Su Qing, Ah Hai, Ming Yue and Dr. K's talks, and the four options on the final screen.
- The twelve echoes: the Echoes codex (bottom-left button, shows n/12), sorted by region, each with a picture.
- 34.2: in no line of dialogue, file or echo — it's 52.9 minus 18.7, the two figures Dr. K gives you.
- The four S/A/B/C grades and the critical-oxygen rule both follow the in-game logic.
Chinese and English lines match one to one.