Casebook Rules and Deduction Guide
From your first clue to the final explanation, learn to read evidence, record deductions and find the person who fits every condition.
What is the goal?
Each case asks a specific question. Use its public rules and all the clues to find the person who fits the conditions, then submit your answer.
You eliminate possibilities using reliable records. You do not need to guess who is lying or add assumptions that the case never states. The target person is unique, although some background arrangements may have more than one valid solution.
Choose your difficulty
| Level | Deductions | Target duration |
|---|---|---|
| Starter | Find the facts. Rule out the impossible. | 1-3 minutes |
| Intermediate | Combine records. Put events in order. | 3-5 minutes |
| Expert | Follow connections through several deductions. | 5-8 minutes |
All three levels are available from the start, with no unlock order. Filter the case library by difficulty, completion status or search text.
The durations in the table are design targets, not averages from player testing. There is no countdown: take the time you need.
Read the public rules, then the evidence
Start with the question, people, time window and any rules for assigning objects or positions. Then read each evidence record. Each case defines its own constraints; do not carry assumptions over from another case.
Open an evidence card for a larger view. Its read marker only means you opened it, not that the game has made a deduction for you. Scene illustrations set the mood; details that are not stated in the text are not evidence.
Use the deduction notebook
The notebook relates people to the attributes in the case. Clicking a cell cycles through three states: · Unknown, × Ruled out, ✓ Possible, then back to Unknown.
These marks are your own deductions. The game does not validate or complete the notebook for you, and Possible does not mean confirmed. Change a mark at any time or clear the notes to start fresh. You do not have to fill every cell before submitting an answer.
Reveal hints one step at a time
Each case has three optional hints, revealed in order. They generally move from a direction to investigate towards a more specific deduction. Revealed hints stay visible, and the number used in this attempt is recorded.
Try connecting the clues yourself before choosing whether to reveal the next hint. Using hints does not prevent you from submitting an answer or completing the case.
Check your answer and close the case
Select a person in the answer area, then confirm your submission. A wrong answer lets you keep investigating and try again. Your notes, read records and revealed hints stay in place.
A correct answer opens the case summary with the target person and a step-by-step explanation. Answer the question the case asks; you do not need to prove that every background arrangement is unique.
Choose Investigate again in a completed case to reset the current selection, notes, read markers and hints. The record that you completed that case remains.
Save, continue and clear progress
When local storage is available, progress is saved automatically in this browser, including your selected answer, notes, read records, hints and completion records. Continue from the library or reopen the same case to resume.
Progress is not synced to a server or another device. When the browser blocks storage, progress lasts only for the current page session. Clearing this site’s browser data removes local records. Clearing progress in game settings also removes completion records and requires confirmation.
Devices, language and controls
Play free in a phone or computer browser, with no account or app installation. The game itself requires JavaScript. Use a mouse, touch or keyboard: Tab moves focus, Enter or Space activates buttons, and Esc closes a dialog.
English and Simplified Chinese are available. You can switch language, light or dark theme, or fullscreen during an investigation while keeping your selected answer, notes and hints.