A mystery focused on identifying the culprit from a group of suspects, with clues planted for the reader to solve alongside the detective.
The whodunit is mystery fiction in its purest form: a crime is committed, suspects are gathered, clues are scattered, and the detective (and ideally the reader) pieces together who did it. The genre runs on fair play, meaning the reader has access to the same clues the detective does. The satisfaction comes from the 'aha' moment when the solution snaps into focus.
Whodunits are the ultimate plotting exercise. Every scene must serve the mystery. Every character must be a potential suspect. Every detail must either be a clue or a red herring. If you can plot a whodunit, you can plot anything.
Ten strangers on an island, dying one by one. The bestselling mystery novel of all time, and the solution is fiendishly clever.
A whodunit where the reader knows who did it from the start, turning the genre's conventions inside out.
A modern whodunit that proved the form is as commercially vital as ever when executed with wit and surprise.
Design a whodunit in outline form. You need: one victim, four suspects (each with motive, means, and opportunity), three real clues, two red herrings, and one solution that uses all three real clues. Don't write the prose yet. Just build the puzzle. If the logic holds, the story will follow.