How to question

Three things you can ask

• Where were you? An honest person says so. The thief names somewhere else.
• Who did you see? An honest person names whoever was at the scene. A liar points at an innocent.
• Know the item? A liar will play dumb. This is where the lie shows.

Asking only where will not crack it

We ran it for real while building the game. Asking only where they were fails on all 90 test days. The thief will never name the scene.

Comparing their stories solves about 60 of 90, and asking about the item solves all 90. It takes five questions on average, so 6 is plenty.

At most two liars

The thief always lies, and one more person may lie too. Three liars never happens. That would make some days unsolvable.

So spot the two liars, then pick the one who was at the scene.

A wrong guess costs nothing

If you accuse the wrong person, you are told where they were. Then you look again and pick again. There is no luck, so the same question always gets the same answer. Asking again is never wasted.

Know what answers look like

Answers come in fixed shapes. Once you know them, the clash is easy to see.

• Where were you? An honest person names where they really were. A liar names a third place, neither the scene nor where they really were. So a liar never says the scene.
• Who did you see? An honest person names whoever was at the scene. If they were there themselves, they say they saw no one. A liar points at an innocent person. If two people name different people, one of them is lying.
• Know the item? An honest person says they know it was at the scene. The thief cannot be honest, so they claim not to know what the item is. That answer stands out the most.

How to spend six questions

Asking one person all three things is slower than asking all four the same thing. That is where the answers clash.

1. Start by asking all four whether they know the item. If one plays dumb, you are done. If two do, move on.
2. Ask the two who played dumb where they were. Both avoid the scene, so this alone will not split them.
3. Spend what is left asking an honest person who they saw. An honest person names whoever was at the scene. That name is your answer.

On days with only one liar, the first question can end it. The average is five.

Common traps

• Asking only where. The most common mistake. It fails on all 90 test days, because the thief will never name the scene.
• Calling every liar the thief. There can be two liars, and one of them just lied without stealing. Whoever was at the scene is the thief.
• Letting a name slip by. The name an honest person gives is whoever was at the scene. Only one person is there, so it is the answer.

Why it can always be solved

Before a case ships, we check that the honest answers alone narrow it to one thief. A case with two people at the scene never goes out. An unsolvable day is not a game, it is wasted time for whoever showed up.

That is also why there are never three liars. With three, there are too few honest answers to check either side.

One case a day, the same for everyone

The case is built from a value drawn from the date. Everyone who plays on the same day gets the same case, so you can compare how many questions it took.

Asking and judging both run in your browser. There is no sign-up, and what you asked never goes to a server.