At the start of The Mermaid Mask, the map opens faster than the case does. A room can look exhausted and still hold the progress gate because the useful state lives on the back of an object, inside its open view, in a conversation unlocked by a new clue, or behind an observation prompt that appears only after an evidence connection.
This spoiler walkthrough covers the prologue and the first full sweep of the Mortuga Submarine: reaching the Illusion Theatre, opening the Control Room, meeting the crew, and resolving the early puzzle states that block those interviews. It deliberately stops before later chapters, the murderer reveal, and the ending. The readable walkthrough evidence available on July 17, 2026 did not support a reliable scene-by-scene route beyond that point.
Release boundary: Steam AppID 1696770 lists the SFB Games release on July 16, 2026 for Windows and macOS. Steam currently reports 21 achievements and supports saving at any time. The route below was checked one day after launch, so use the current client’s labels and visual confirmation if a puzzle presentation changes in a patch.
The first case gate is information, not distance
The opening investigation runs on a repeatable loop. Search a room, manipulate every clue far enough to reveal its hidden state, then take that information back to anyone who has a relevant dialogue topic. An item is not finished merely because it entered the Case File. Books have pages, containers can open or shut, and 3D evidence can reveal an observation only after rotation.
Use four checks whenever the map offers several rooms but no obvious objective:
- Finish the object. Read both sides, open it, rotate it, and move the cursor over any scratch, seam, picture, or moving part that receives a reaction.
- Finish the witness. Ask the basic questions, the suspect questions, and every clue topic currently visible. A greyed or locked topic usually means the case state is incomplete elsewhere.
- Revisit after a new name. Learning who a person is can change a room that previously contained only a painting, a pair of eyes, or an inaccessible door.
- Revisit after a new object. The Glass Eyeball, underwater photograph, broken compass, and recorded pipe each become more useful when shown to the right person.
This is also the safest achievement habit. Steam’s 21-achievement total includes story and optional interactions, but the supplied achievement page was not readable. Inspecting first and advancing second preserves more opportunities than racing between highlighted exits, without pretending this early route is a 100-percent checklist.
From Stonetop Inn to the cauldron scratches
At Stonetop Inn, examine the copy of Hex of the Helmsmen and open the red Case File before waking Sally. The file establishes Captain Magnus Mortuga’s locked-room death and gives the detectives their initial reason to find Captain Seafoam. Once Sally is awake, open the map and choose the unknown Town Square location.
In the square, inspect the signs and speak to Sally, then select the green light in the water. That action brings the Mortuga Submarine into view. On the fore deck, examine the wooden buoy with glowing eyes before using Sally to descend. The Parlor starts in darkness; the light lever reveals the room, but the Control Room remains blocked by a notice and a watcher you cannot yet identify.
Go to the Mess Hall and inspect the table, cookware, lights, and the snake-shaped cabinet. Its four dials use polygon corners as values: a triangle contributes 3, a square 4, and a pentagon 5. Rotate the layered shapes so each numbered window receives that corner total. The useful combinations are 3 = triangle, 4 = square, 7 = triangle plus square, and 9 = square plus pentagon. A triangle plus pentagon totals 8, so it cannot satisfy the 9 window even if an old written hint suggests it.
The opened cabinet yields the Sun Tablet bottle. Continue to the Illusion Theatre, where the murder evidence is concentrated. Inspect the stone cauldron and rotate it until the deep interior scratches become selectable. Examine the broken bottle marked with a moon, the broken stool, the torn cloth with writing on its reverse, the upside-down poster, and the chalk outline. Compare the stool with the one at Stonetop Inn when the Case File asks for a match.
For the first evidence connection, build the theory that Mortuga opened the cauldron and the lethal threat came from inside it. The game then asks what Grimoire noticed. Return to the 3D cauldron, rotate toward the marked interior, and select the scratches. That observation closes the prologue and changes which rooms and people can respond.
Turn six cards into the Glass Eyeball
Enter the Child’s Room to the left of the Illusion Theatre. Read the newspaper on the shelf, including its reverse, then open the box covered with cards. The puzzle contains six picture halves and four lenses. Solve the pictures before touching the glass: pair the halves into three complete girl-and-doll scenes and arrange those three scenes in a row.
The written clue separates the middle child from the jealous pair. Patricia’s doll is neither enlarged nor reduced, so her completed scene belongs in the neutral middle position. Put the magnifying and reducing lenses over the dolls in the two outside scenes. The two fish-eye lenses belong over the faces of those outside girls. Leave the middle girl’s face and doll without a lens.
The reward is a Glass Eyeball. Return to the Parlor and check the eyes watching through the Control Room door. The unseen person points you back toward the Child’s Room. The painting there is now interactive: it is Symmetry Silkmoth. Ask her about herself, the submarine, and every available suspect and clue. Do not worry if her final suspicion topic remains locked; the rest of the ship has not yet supplied enough evidence.
Open Sinthia’s room, then reopen every conversation
After identifying Symmetry, go back to the Parlor watcher. Sinthia Seafoam will open the Control Room. Complete her introductory, suspect, and evidence topics before treating the room as a puzzle space. Then inspect the submarine blueprint, the wheel, the captain’s jacket, and the control panel.
The switchboard asks for six colored plugs to be placed in the sockets that activate the screen. The readable text source confirmed the gate and reward but did not preserve a trustworthy socket-by-socket layout, so use the current board’s color paths and illuminated feedback rather than a guessed fixed map. When all six connections are accepted, the hatch opens and exposes the Captain’s Log. Read the log fully, then show the new Control Room evidence to Sinthia and Symmetry.
Symmetry’s response points toward the shared bunk. This is the important handoff: the Control Room is not finished when the hatch opens; it is finished when the resulting log and personal details have created the next searchable state in the Bunk Room.
Clear both bunk rooms without treating every prop as evidence
In the bunk shared by Sinthia and Symmetry, read the movie magazine and manipulate the pink piggy bank. Its red numbers are fixed targets. Rotate or move the seven body parts until the visible values built by those parts add to each target. The useful rule is arithmetic, not the pig’s final pose; confirm each number before moving to the next segment.
The bank contains an underwater photograph. Show it to both Sinthia and Symmetry. Sinthia identifies its connection to the day of the murder, while Symmetry’s reaction points toward a hiding place beneath Sinthia’s mattress. Return to the bunk and search there for the Inn Deeds. Read the document before questioning Sinthia again; it links Mortuga to Stonetop Inn and creates a more useful contradiction than the photograph alone.
The neighboring bunk introduces Dirk Dansom and J.D. Wirman. Exhaust both interviews first, because their answers give context to objects that would otherwise look like set dressing. Dirk’s phone uses four silhouette-matching pieces; complete the shapes, then read the calls, messages, and email rather than closing the device after the lock disappears.
Wirman’s typewriter is a rotation problem. The strip at the bottom supplies related versions of the same symbol, while three dials change the central display. Read each adjacent pair as stages of a 45-degree rotation and set the middle version between them. A surviving Steam guide describes this relationship but is marked removed and incompatible, so this guide does not publish a supposedly permanent dial count. Follow the rotation relationship visible in your current puzzle and take the handwritten letter addressed from Ibis.
Finish the lower-deck witness loop before solving the pinboard
Visit the Dream Chamber and question Doctor Zephyr. Inspect the Hex Bottle, Dream Helmet, and Fog Ball, then reopen his clue list after each item joins the Case File. The goal here is not to decide whether the dream science is credible. It is to make sure Zephyr’s account and every object are available for later comparisons.
In the Cargo Hold, interview Mariana Moon and inspect her belongings. Take the Silkwirm map, but leave the large pinboard until the roster is complete. The board represents who is aboard and where people are now, not the murder-day timeline Mariana is recounting. Solving it too early turns a current-position puzzle into a memory test with missing subjects.
Keep presenting the Glass Eyeball until its purpose becomes clear, then use it on the Captain’s Cabin door. Inside, find the broken handheld radio in the chest, inspect the bell, examine the ship in a bottle, and record the painting titled Her. Open or rotate each clue where the Case File permits it. The cabin sweep is valuable because it creates several new questions for witnesses who previously had nothing more to say.
Move to the Engine Room and inspect three of Godrik Gripp’s wares to push the encounter into a proper interview. Ask about his stock, the suspects, and the evidence. The moving compass puzzle is governed by four personalities rather than ordinary north: one tries to point away from the group, one refuses to participate, one behaves as a clock, and one points toward the others. Use those behaviors to identify the intended positions. The reward is the broken compass being repaired beside Gripp.
Return to Mariana after the compass conversation. Her wooden pipe is not merely a pipe; it records voices. Listen to the captured exchange, then revisit the Illusion Theatre. A spot in the left wall now reveals another mechanism. Expose it, but do not assume it must be solved immediately; the first sweep still has one witness missing.
Go to the Airlock Grotto and speak with Madam Tadpole. Complete the basic, suspect, murder-day, and clue topics. Her account of a glowing-eyed figure on the fore deck can now be compared with the strange sighting reported elsewhere. At this point you have met Symmetry, Sinthia, Dirk, Wirman, Zephyr, Mariana, Gripp, and Tadpole.
Now the Cargo Hold pinboard has a complete set of living subjects. Place the crew according to their current rooms on the map. Do not force Mortuga into a cabin: he is dead and no longer occupies a current ship position, so leave him off the active layout. This rule survives in a warning-bannered community guide and should be treated as a logic check, not as authority for exact pin coordinates.
Use this stalled-state checklist
| What appears stuck | Case state to inspect | Next action |
|---|---|---|
| The Control Room watcher will not open the door | The Child’s Room box, Glass Eyeball, and Symmetry introduction | Finish the card-and-lens puzzle, inspect the Parlor eyes, return to the blinking painting, and exhaust Symmetry’s available topics. |
| Symmetry’s suspicion topic remains locked | Unmet crew and unpresented evidence | Continue the first ship sweep. A locked suspicion is not proof that the Child’s Room puzzle is wrong. |
| The Captain’s Cabin will not open | Whether the Glass Eyeball has been discussed and then used on the door | Present it around the ship until its key function is recognized, then select it at the cabin entrance. |
| The underwater photograph changes nothing | Separate reactions from Sinthia and Symmetry | Show it to both, then search beneath Sinthia’s mattress for the deeds. |
| The Cargo Hold pinboard has too many uncertain pins | Whether all eight living crew members have been met | Visit the Airlock Grotto and any unopened room first, then place people by current location and leave Mortuga off the ship. |
| A room is clear but the story does not advance | Unread backs, unopened views, unrotated 3D clues, and stale witness menus | Finish the object states, then make one evidence-presentation circuit through the relevant crew. |
Watch the demo route without confusing it for the full case
The video below was independently verified through YouTube oEmbed as The Mermaid Mask | FULL DEMO | No Commentary by SUBWAY CIRCUIT. It is useful for checking the prologue’s room transitions and interaction targets, but it is a demo recording, not evidence for the later full-game chapters covered by neither readable walkthrough source.
What this walkthrough deliberately stops before
The Neoseeker walkthrough hub, prologue, first chapter, and achievement pages all returned a Cloudflare verification shell during research, including a reader fallback. The readable walkthrough set ends after Madam Tadpole and the first crew sweep. It does not establish the later chapter order, final accusation, murderer, ending logic, or a complete 21-achievement route.
That boundary matters more than filling the page with unverified solutions. At the end of this route, your useful state is specific: the prologue theory is registered, the Glass Eyeball has opened the cabin, the Control Room log is read, both bunk rooms are searched, the lower-deck crew is interviewed, the pipe recording and broken compass have been found, and every new clue has been carried back through the relevant conversations. Continue from the next live objective in your client rather than treating an unsupported ending guess as a walkthrough step.
Sources & credits
Game identity, Steam AppID 1696770, SFB Games developer and publisher credit, the July 16, 2026 release, Windows and macOS support, save-anytime feature, 21-achievement total, and the five original 1920-by-1080 JPG screenshots were verified against the official The Mermaid Mask Steam page. Studio ownership was cross-checked against the official SFB Games site, whose pre-release wording was not used for current availability. Puzzle order and early investigation checkpoints were reconciled across readable walkthrough references; removed or incompatible community guides were used only for explicitly limited logic checks. All public images remain unmodified Steam JPG files supplied by SFB Games.