Last week I was musing about romance tropes - the scenarios that let readers know what they will be getting when they pick up a book. It's a topic often discussed.
Crime tropes - not discussed so much, but I think they do exist,
I've had a go at a list.
Death/murder - there can be books with other crimes. but let's face it we do like a dead body, or five.
Troubled protagonist - addiction, marriage problems, loner
Unidentified victim - need to determine who your dead body is before you can find out who killed them. A classic on this one is Agatha Christie's Body in the Library. Where the hapless Colonel and Mrs Bantry have no idea who the dead girl is. Enter Miss Marple, stage right ...
Mysterious poison - more of a Golden Age motif as forensics advance
Lost heir - Josephine Tey's Brat Farrar is a classic. Can only be historical now, with the arrival of DNA testing.
Forced proximity - this one can be a romance trope too - in the crime case it is a group of people cut off from the outside world - snow, floods, And you know what will happen - And Then There Were None ...
Courtroom dramas - a trope or a setting?
Unreliable narrator There is a classic on this - Dame Agatha again, but I won't risk a spoiler.
Amateur sleuth beloved in 'Cosy' mysteries. These days they often have lifestyles/hobbies that add to the layering - dog walker, gardener, baker.
Falsely accused who has to be exonerated.
The Too Stupid to Live Victim. The one who goes into the creepy empty house when there is a serial killer on the loose.
A villain who taunts the police
A key witness who lets it be known they have information but delays to allow enough time for them to become the next corpse. (I really hate that one!)
I'm sure there are more, but that's not a bad start!