How to play Casebook

Every case has three people, three places and three objects. During the case, each person was in exactly one place and had exactly one object, and no two people shared a place or an object. Your job is to work out the whole arrangement from the clues, then say who is responsible for the incident.

The clues

Every clue is true and says exactly one thing. There are three kinds:

• A person and a place: “Ada was not in the archive.”
• A person and an object: “Basil had the spare key.”
• A place and an object: “The lantern was in the lighthouse.” Objects stay with whoever has them, so this means the person in the lighthouse had the lantern. “Whoever was in the hall had the tuning fork” says the same thing.

There are no liars, no hidden times and nothing to know from outside the case. The story sets the scene but never adds a clue of its own. The clues alone always lead to exactly one arrangement.

The incident

The “What happened” note names one place and one object. The responsible person is whoever was in that place and had that object. Fill in your notebook first, then find the card with both.

Your notebook

Each person has a card with their places and objects. Choose what a tap does with Mark yes (a tick) or Rule out (a cross), then tap a square. Tap it again to clear it. The “Where was each object?” card is optional, for clues about places and objects.

Casebook never changes your marks for you. If two marks clash (two people in one place, say), both turn red and the card tells you why. Marks are saved in this browser after every tap.

On a keyboard: Tab or the arrow keys move between squares, Enter or Space applies the current mark, Y ticks, X crosses out, and Backspace clears.

A worked example

Clue: “Ada was not in the reading room.” Clue: “Ada was not in the archive.” So Ada was at the front desk, the only place left. Then nobody else was at the front desk.

The first tutorial walks you through a whole case like this, one mark at a time.

Hints and the solution

A hint shows the next step that follows from the clues, names the clues it uses and highlights the square to mark. If one of your marks can’t be right, the hint offers to point it out first. Hints are counted in your result. You can also reveal the whole solution; that attempt then counts as revealed rather than solved.

Closing the case

When every person has one place and one object ticked, choose Close the case and pick who is responsible. If something doesn’t fit, you’ll be told to check your deductions, and your notes stay as they are. There’s no limit on tries. When you get it, Casebook shows every step of the reasoning.

Difficulty

• Introductory cases give you at least two direct facts and need only simple steps.
• Intermediate cases need you to combine a place with a “not” (“Ada was in the hall, and the key wasn’t in the hall, so Ada didn’t have the key”), or start from almost nothing.
• Advanced cases give at most one direct fact and no free starting point; some need you to suppose something, follow it to a contradiction and rule it out.

The daily case and streaks

A new daily case starts at 00:00 UTC, the same for everyone. Solve it on its day to keep your streak going. If you start it on its day, it still counts if you finish by 02:00 UTC the next morning. Past dailies are in the archive; playing them is labelled as an archive replay and never changes your streak. Every case can also be played as practice at any time. Your result counts tries and hints; time is shown for interest only.