How we change what others think, feel, believe and do
A crime is committed.
The detective patiently and brilliantly examines and follows clues, eventually deducing whodunnit.
The person who committed the crime is arrested or otherwise meets a sticky end.
Sherlock Holmes solves many whodunnit mysteries, showing his brilliant deduction at every step.
Agatha Christie's Poirot is another annoyingly clever detective who lacks a winning personality yet who you cannot help but admire.
Columbo uses a neat reversal where you know who dunnit from the beginning, but still can enjoy the story from a position of knowing.
'Whodunnit' is short for 'who done it', which is slang for 'who did it'. It is the question that is usually on everyone's lips throughout the story.
The game with the reader in this story is that the reader is teased into trying to guess whodunnit. In a good story, the reader gets close but does not guess in time, yet when the criminal is revealed, the reader thinks 'of course!'.
Some authors (including Agatha Christie) use the same story pattern so often that whodunnit is quite easy to guess (often the most unlikely person), making the story less enjoyable.
In a twist of the storyline, the reader finds out early in the story whodunnit. The tension in the story is subsequently gained from the frustration of the reader at the 'near misses' and other problems that the detective experiences in identifying the criminal.
Further tension may be derived if the criminal is plotting to do it again.
In change stories, the whodunnit format can be used to mirror mysteries such as business problems and derring-do in the marketplace.