The (Classic Doyle) Howdunnit Formula

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Solving “impossible crimes” was one of the things Holmes was most famous for, and Doyle was fond of coming up with puzzles to challenge his great creation. In fact, a good way to think of a howdunnit is as it being a puzzle.

“How did the killer get in and out of the locked safe with guards around it?”

“How did the thief cover the distance between a party and the crime scene faster than a car can travel?”

“How did the victim die without leaving any evidence behind?”

The answers to these puzzles will lead to solving the crime, and preventing the criminal from getting away with their immoral actions. Maybe it will stop them from killing again? Maybe it will prevent them from getting on a plane to freedom? Either way, the puzzle is the key.

In Doyle’s case, a howdunnit usually runs something like this…

Introduction (15% or less of the story, 900 words in a 6000 word story)

  • The main detectives are introduced in an interesting way which shows off their personalities.
  • A new character with a problem (hereafter called the “innocent”) appears before them and the main detective character shows off their detective skills by guessing information about the Innocent.

The Situation (35%, 2100 words)

  • The Innocent tells the detective characters about their problem. The innocent tells them the details of what happened which lead them to coming to see (or calling for) the detectives.
  • A crime has been committed, and usually there is only one main suspect, but there is no proof they did it and the detective must figure out how the crime was committed to stop them from committing another crime or getting away.
  • The Innocent will tell the detectives their story, which will include all suspects (although they may be under fake names), the important details of the events they’ve experienced, and a few important clues (which they might not realize are clues and just think are details). The detective will catch these clues, but probably won’t put them together or mention this to the audience. The clues should be worked into the story in such a way that they don’t stand out as being clues and fit in with the rest of the Innocent’s story unless the audience pays very careful attention.

The Investigation (20%, 1200 words)

  • The detectives will take action to help the Innocent, usually by going out and gathering more clues or information.
  • If there’s not a lot of information, then we might follow the main detective and their partner as they talk to various people involved in the case. They may interview witnesses, examine crime scenes, or collect the stories of the people involved.
  • If there’s a lot of information to be gathered from various sources, the main detective and their partner may split up and then meet again later to compare notes. This is to speed up the process of telling the story by having one or both of them summarize the information they learned for each other and the audience.
  • Often the case will get stranger, or there will be a twist, near the end of this phase (but not always). The most common twist is the elimination of the “red herring” where the most likely method of committing the crime is eliminated as the way it was done. 
  • At the end of this phase, the main detective (and the audience, maybe) will have the key information they need to solve the case and will often say that they know to their partner. (But not tell the audience what they’ve figured out.)

The Reveal (30%, 1800 words)

  • The main detective will now take steps to catch the guilty party.
  • The detectives will set a trap for the criminal, usually by getting one step ahead of them and laying in wait. If the criminal is using the same “secret method” again, the detectives will often replace the victim to catch them in the act and then reveal how the criminal made a mistake that let them get a step ahead and prove the criminal’s guilt. If the criminal had a perfect crime, the detective will trick them into thinking they made a mistake, and then catch them when they try to cover up the mistake or flee. Confronted with the truth, the criminal will confess all, or if they died as the “secret method” kills them instead of their intended victim, the detective or someone else will fill in the missing pieces.  
  • With the crime laid out, the audience should be able to look back now and see clearly how everything fit together in a reasonable way. There should be no magic powers, acts of god, or huge co-incidences, and everything should make sense.
  • Usually, there is one last unanswered question, and in the final scene the detective’s partner or the Innocent asks it to the main detective, and the detective answers them in some interesting way. The final scene usually ends on either a final thought or (in later stories) on an amusing note to balance out any tragedy which the ending revealed with positive emotions.

One interesting feature of a howdunnit is that they are sometimes played as a sort of duel between the detective(s) and the culprit. The culprit is often (but not always) an active character in the story who the detective is interacting with and the detective gets to know as the story goes on, and since howdunnits can more easily be victimless crimes, the culprit might even be sympathetic in their goals. Or, the criminal may be a very unlikeable person who taunts the detective with their lack of proof and angers the audience like a true villain until the detective finally outwits them in a final display of brilliance or skill at the end.

The challenge with writing howdunnits is to come up with a puzzle that isn’t too easy for the audience to figure out while giving them enough clues to make it possible to solve before the end. Even Doyle didn’t always play fair in this regard, and sometimes slightly cheated to make sure the audience couldn’t guess until the end. However, whenever possible you should avoid doing that if the puzzle is the main question you build your story around.

A suggestion for writing these stories is to come up with the method for doing the “impossible crime” first, and then figure out what kind of crime it’s best used with. However, whatever method you use to plan it, thinking through the crime before writing is a must!

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