Sealed Mystery
Blackfile №1: The Vanishing at Larchmont Hall
The heiress vanishes from a bolted conservatory of a 1920s country house; the answer was sealed before you arrived, and the AI cannot change it.
Blackfile №1: The Vanishing at Larchmont Hall is a free murder mystery you play inside ChatGPT, Claude, or Gemini. A 1925 locked-room whodunit: an heiress bolts a glass conservatory from the inside and is not there when the doors come down. Solo, 60–90m a run. No signup and no app — open it in your assistant, or paste the play prompt anywhere else.
- Players
- 1
- Length
- 60–90m
- Rating
- 12+
- Version
- 1.1.0
Works with ChatGPT · Claude · Gemini. Free, no signup.
Opens your assistant with the game loaded. ChatGPT usually runs it straight away; Claude waits for you to press send. Same link on your phone as on your desktop. Playing in Gemini? Tap Copy the play prompt and paste it into a new chat. What works where.
No web access, or want it as an installed app?
The game card is the entire game — every scene, rule and answer, about 13k characters. Paste it when your assistant can't browse the web. The Skill installs Blackfile №1: The Vanishing at Larchmont Hall into Claude on any plan: download it, then turn on code execution under Settings → Capabilities and add it at Customize → Skills → + → Upload a skill.
How to start
- Open your AI. Start a new chat in ChatGPT, Claude, or Gemini. No paid plan required.
- Paste the case file. The file includes the sealed hash and boots Larchmont Hall the night of the vanishing.
- Investigate. Question suspects, examine rooms, and follow the timeline. The AI answers only from the sealed facts.
- Accuse and verify. Name the culprit, then hash the revealed solution to confirm it matches the seal.
Questions
- How do you stop the AI from making up the answer at the end?
- What became of Iris Larchmont — how she left a bolted glass room, and why — was written out and hashed with SHA-256 before this card went public, and that hash is printed in the case file you paste. The AI reasons from that fixed text and nothing else, so it cannot quietly settle on whichever suspect you have been circling all evening. When you accuse, you can run the reveal through SHA-256 yourself and hold it against the printed commitment.
- What does a sealed solution mean?
- It means the ending is fixed in advance. A SHA-256 hash commits to the solution at the start, so the culprit is decided before your first question. When you finish, the reveal matches the seal, which makes the mystery fair and verifiable.
- Can I solve it, or does the AI just tell me?
- You solve it. The AI plays the house, its suspects, servants, and physical clues, and answers what you investigate, but it will not hand you the culprit. Make your accusation when ready; the sealed file confirms whether you were right.
- What happens if I accuse the wrong person?
- You get one accusation and it stands. The seal opens either way — the GM reads out what actually became of Iris — and you score the clues you turned up, plus five for naming it right. If you are not ready to speak, say "save" instead: the case prints a code that carries your clues into a fresh chat alongside the file.
12+ — no violence and no death; includes a woman covertly dosed with a 'nerve tonic' and a coercive betrothal.