A good mystery is all about the question. If the protagonist is a criminal then the question is “how will they accomplish the difficult task”. If the protagonist is a detective then the question becomes “how did they do it”. In both cases the beginning establishes how difficult the task is or was, then spends the rest of the story gradually dropping hints and clues, giving audiences the chance to try and solve the mystery. The key is to carefully manage information so that audiences feel like they have a chance, but don’t solve the mystery before the end of the story. Many mysteries use comical side plots to break up what can be a dry main story.
Mystery, Thriller, Horror, Scifi, & Fantasy 109-03