GenresFiction
Mystery
A question that must be answered.
A mystery makes a promise that something will be found out. It might be who did a thing, or why a person vanished, or what a town has agreed not to say. Readers are playing along, which means you owe them fair information. You can mislead them, and you should, but the answer has to be made of pieces that were actually in the book, not a relative who walks in on page three hundred with a confession nobody could have guessed.
The detective, professional or not, needs a reason to keep going when it would be easier to stop. Curiosity is enough if you make it personal. Setting helps more than people admit: a village, a precinct, a ship, a university, anywhere the suspect list is limited and the relationships are already tangled. Write the clues so they mean one thing the first time and another thing later, and don't hide the only important object in a sentence you hoped the reader would skip.
The kinds of book inside it
Cozy
The violence is mostly offstage, the detective is often an amateur, and the community is half the pleasure, so the book can be warm without being soft about the crime.
Detective
Someone's job is the case, and the interest is as much in how they think as in the answer they eventually reach.
Amateur sleuth
The sleuth has another life, which is useful, because their access to the truth shouldn't look like a police warrant.
Police procedural
Procedure is part of the texture, interviews and paperwork and the limits of what an officer is allowed to do, and the team matters.
Locked room
The impossibility is the point, so the solution has to be clever and physical, not a shrug about magic unless magic was always in the rules.
Historical mystery
The investigation has to work with the tools of the time, and the period should make the crime harder, not just prettier.
Noir
The world is compromised, the detective may be too, and the answer often costs someone more than it repairs.
When you want a first sketch, Storywell can draft a story summary in this vein. You are still the one who writes the book. Compose an idea.