Sealed Mystery
Blackfile №1: The Vanishing at Larchmont Hall
A guest vanishes from a locked wing 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 1920s locked-room whodunit whose culprit is sealed before you start. For solo play, about 1–2h a session, it needs no signup — paste one game card into your assistant to play.
- Players
- 1
- Length
- 1–2h
- Rating
- 12+
- Version
- 1.0.0
Works with ChatGPT · Claude · Gemini. Free, no signup.
Open in ChatGPT Open in Claude
Opens your assistant with the game loaded — review the prompt, then send.
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?
- The full solution, culprit, method, and motive, is written before you play and locked with a SHA-256 hash printed in the case file. The AI reasons only from that fixed text, and you can hash the revealed solution yourself to confirm it never changed.
- 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.
- Do I need an account or any tools?
- No account beyond the chat app. Paste the case file into ChatGPT, Claude, or Gemini to begin. Verifying the seal uses any SHA-256 tool, including ones built into your operating system, and a save code lets you pause and resume the investigation.