Actually Solving “Reader-Solvable” Mysteries

The Plague Court Murders by John Dickinson Carr is a 1934 classic reader-solvable mystery. Spoilers: With characters swapping outfits, melting bullets, and a chapter-long red herring, I was at a loss for how anyone could figure out whodunit.

Have people actually found the solution before the end of the book, or is “reader-solvable” just marketing to make us feel like we’re learning to be clever detectives?

I decided to take out the big guns (a pen and paper) and make a serious effort at solving mystery fiction before the ending reveal.

Here are the rules I set for myself:

  1. Make a table with a row for every suspect. Leave plenty of space between each row to write notes. The columns are “Character,” “How,” and “Why.”
  2. Everyone with a name is a suspect except the point-of-view character and the “famous” detective character (e.g. Sherlock in Sherlock Holmes). Characters without names (e.g. “the butler”) may also be suspects if repeatedly referenced.
  3. The only accepted facts are things the narrator sees or the “famous detective” character states. I’ve found that you can generally rely on the “famous detective” to be correct, whereas the narrator can be deceived about things they didn’t see. All other clues must have their source recorded (e.g. “the butler said”).
  4. You must mark a guess at the culprit(s) every chapter.

My strategy was to accuse a character with a strong “How” and “Why.” If no one fit, I would start looking for combinations of characters and accuse them all.

            |        How       |       Why
------------|------------------|-------------------
Character 1 | |
| |
------------|------------------|-------------------
Character 2 | |
| |
------------|------------------|-------------------

I wanted to test this framework on lots of stories in a short time, so I checked out an Agatha Christie collection from my library. Besides the fact that her work is recognized as reader-solvable, I picked the “Dame of the British Empire” for another reason: revenge.

It wasn’t my first time trying to solve mysteries, and I distinctly remember Agatha Christie’s collection of Miss Marple stories. In each tale, the main character, Miss Marple, sits in a room with half a dozen guests, and they all guess the answer to a mystery. Miss Marple inevitably provides the answer after every other guest is wrong.

The moment one of the dinner guests said what I was going to say, I realized Christie had not only fooled me, but she knew exactly what trap she had lured my mind into. She repeated this feat for each story in the collection.

Well, not this time, Agatha.

Story One

The first story revealed a problem with my table-based strategy. I always had to assign clues to at least one character — there was nowhere else to write them. It’s a mixed blessing and curse because the restraint forced me to constantly make “How” and “Why” connections but also assign seemingly-unrelated clues to individuals.

Also, the short stories turned out not to have sections, so I update my rule to force myself to make a guess every 2–4 pages.

Did I guess the killer? Kind of. I caught one killer, one accomplice, and accused a perfectly innocent person. My final guess was that a trio did the crime, but it was actually a duo.

Stories 2–6

For the next five stories, the strategy worked pretty well. I got whodunnit for three stories but only one howdunnit. I could generally tell which characters were the sketchiest but couldn’t guess how they committed the crime.

Catching the culprits at all was totally new for me. Maybe I should have been celebrating, but my “How” and “Why” tables were a mess. If a clue didn’t fit the “How” and “Why” of any suspect, I assigned it to the victim because there was nowhere else to put it.

Also, I found that the supporting character, Inspector Japp, could be trusted not to commit crimes, so I stopped giving him a row in the suspect table.

Stories 7–9

For the seventh story, I decided to add a clue log. This bullet-pointed list would sit on a separate page and host all the general facts.

I also expanded my definition of “How” and “Why” to include their opposites. For example, in “How,” I might write, “the doctor had access to poison” but also “the doctor claims he had never treated the victim.” I used plus or minus symbols for facts incriminating or defending a character.

Toward the end of the seventh story, I changed my guess from the correct killer to a newly introduced character. Poor choice. The culprit is rarely someone introduced past the 50% point. The main exception to this rule is if a late-introduced character turns out to be the same person as someone introduced earlier.

For the eighth and ninth stories, I got whodunnit but not howdunit.

Stories 10-25

From the tenth story onward, I conceived a new approach. I would keep the clue log for the most generic facts, but each row in the character table would have “Facts” and “Theories” columns instead “How” and “Why.” Example:

            |      Facts       |    Theories
------------|------------------|-------------------
Character 1 | |
| |
------------|------------------|-------------------
Character 2 | |
| |
------------|------------------|-------------------

Remember, facts need labelled sources unless they are from trusted characters (in my case, the narrator, Hercule Poirot, and Inspector Japp).

After reading the rest of the short story collection, I was happy with the system. I guessed whodunnit and howdunnit for seven stories and whodunnit alone for one story. I awarded myself one point for each of these.

There were four stories where I was one suspect too short or too many, so I gave myself half a point on each. I also eliminated three stories because they were more adventures than solvable mysteries.

Adding this up, we can informally give the strategy a score of 9/13 or 69%. Of course, I might have just been getting better at understanding Agatha Christie’s writing patterns over time. Still, not bad for someone who has never solved a reader-solvable mystery in his life.

Let me know your approach to one of my new favorite games.

Interested in too many things.

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