The Thirteen Problems (Miss Marple), by Agatha Christie
Bored, a group of people are thinking of ways to entertain themselves and they somehow manage to land on the intriguing topic of murder. They find the topic of murder fascinating in a morbid sort of way. They come up with a kind of game. Each person is to take turns and tell the others a mystery, and not just any mystery but a murder mystery. It has to be true and only they knew the identity of the murderer. At the end, the others have to guess who the murderer is. That is literally the plot of the entire book, except for a murder that is committed at the end. It wouldn’t be an Agatha Christie novel without a murder. The game is played on two separate occasions with different groups of people, but the concept is the same.