The Cast

Characters & Suspects

Who's who aboard the Mortuga submarine — the investigators, the victim and the eight suspects with motives and alibis.

The investigators

| Character | Role | Notes | | --- | --- | --- | | Detective Grimoire | Player protagonist | Hired by Sinthia Seafoam to investigate the locked-room murder. He breaks the case by interrogating suspects, collecting clues and reconstructing the truth. | | Sally Spears | Grimoire's partner | Returns from previous games; provides hints and comic commentary throughout the investigation. |

The victim

| Character | Role | Notes | | --- | --- | --- | | Captain Magnus Mortuga | Murder victim | Found dead in the locked Illusion Theatre beside an ancient stone cauldron. Former captain of the Mortuga submarine. |

The suspects

  • Sinthia Seafoam — Acting captain. She hired Grimoire to investigate. Taking command so quickly after the captain's death makes her a primary suspect. Linked to the Inn Deeds.
  • Symmetry — Illusionist / magician's daughter. Her magic act equipment is found in the Illusion Theatre. Linked to the Golden Locket.
  • Zephyr — Dream Chamber occupant. Associated with the Dream Helmet and perfume bottles.
  • Dirk — Engineer / bunk room occupant. Owns the cellphone used to light the Bilge.
  • J.D. Wirman — Author / bunk room occupant. Owns the typewriter; wrote the novel Hex of the Helmsmen.
  • Gripp — Engine Room worker. Knows the submarine's movements; needs to be questioned repeatedly.
  • Mariana Moon — Cargo Hold / performer. Hides a pipe-shaped dictaphone with secret recordings.
  • Tadpole — Airlock Grotto diver. Provides the birthday clue needed to unlock the Pocketbook.
This is a closed case: every suspect, clue and motive is contained within the game's own scenario, so no outside knowledge is needed to solve it. Although Sally and Grimoire return from earlier games, The Mermaid Mask is a standalone story — no prior playthrough required.
Advertisement
Ad placeholder (adsense)

Sources: ninewiki.com walkthrough, 2026-07-17; grindnstrat.com puzzle solutions, 2026-07-18; themermaidmask.wiki, 2026-07-18.

Advertisement
Ad placeholder (adsense)