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The Smoke Man and the Vault (illustration)
FILE No.14Unsolved

The Smoke Man and the Vault

Difficulty ★★★about 6 minLocked Rooms & Impossible CrimesReading rules exactlyElimination
In a world where some can turn into smoke, a man is killed in a locked vault. Apply the special rule exactly to find the culprit.

Case Record

In a certain world, a few people have the ability to “turn into smoke.” A person with the ability can turn their body into smoke for at most one minute at a time. After using it, they must wait three minutes before they can use it again. But only the body changes; clothes and belongings do not change with it.

In a locked vault, the master of the mansion was struck dead with an iron paperweight. The entrance door was locked, but near the ceiling there is a ventilation duct 25 cm wide and 12 m long. The paperweight, the weapon, was left on top of the safe.

There are three suspects: Haitani, who can turn into smoke; Nagano, the butler, who held the key to the door; and Takeuchi, the master’s nephew, who had just arrived at the mansion.

Haitani claims, "I can turn into smoke, but I cannot go through the duct carrying a paperweight." Nagano says, "I had the key with me the whole time." Takeuchi says, "I know nothing."

Your question

Taking the special rule into account, who is the most plausible culprit?

Case Files

Evidence

Diagram

Diagram

Timeline

  1. The master goes into the vault.
  2. The master’s body is found in the vault.
  3. The door is locked. The weapon is still on top of the safe.

Hints

If you get stuck, open the hints one at a time, in order.

Open hint 1

Only the “body” can turn into smoke. What happens to the clothes, then?

Open hint 2

If Haitani had left through the duct wearing clothes, something odd would happen.

Open hint 3

The weapon was left at the scene. It is a crime that did not need to carry it out.

Solve It

Your question

Taking the special rule into account, who is the most plausible culprit?

Choose the answer closest to the truth.

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The Truth

Nagano, the butler who held the key

The answer is “Nagano, the butler who held the key.”

If Haitani went through the duct, it would take about a minute even as smoke. The ability lasts at most one minute, and only the body changes, so he could not carry the paperweight through. In this case, though, the weapon was left on the safe, so it did not need to be carried out after the blow. Even so, Haitani cannot be the culprit. After the crime he could leave as smoke, but his clothes and belongings do not change with him, so he would have to leave his clothes in the vault. No clothing was left at the scene. Nagano, who held the key to the door, could simply enter and leave normally and lock the door again. The more conspicuous the ability, the harder it is to see the person who does not rely on it.

Who can do itHaitani: clothes would remain in the vault; none were foundTakeuchi: no access and no motive shownNagano: has the key, enters and leaves normally, locks againAnswer: Nagano, the butler
Diagram of the solution

Key Points

  • Read the special rule word by word (“only the body” decides it)
  • The person with the flashy ability may be the one to rule out
  • A “person with the key” can come and go without any ability

Why people get fooled

When a special ability appears, you want to explain the case with it. But applied exactly, the rule shows the person with the ability is unsuited to the crime.

Similar tricks

  • Elimination using a special rule
  • The type where a flashy element is a decoy

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