Someone is murdered. The detective assembles the clues and a cast of potential murders. Motive. Means. Opportunity. But the clues don't make sense. Everyone has reason and alibis. Suddenly it all makes sense. There is rhyme and reason. Of course, the reader is still in the dark as is everyone else. The suspects are gathered; the clues laid out. Then the detective explain everything. Finally the accusation is made. The murderer fesses up and is arrested. Another mystery solved and bad guy is brought to justice.
Naturally twists abound. In Agatha's Ten Little Indians, one by one suspects are picked off until there are only two. And each suspects the other. Murder on the Orient Express has twelve suspects or was it a stranger? In all she wrote 91 books under her own name and pen names.
I wrote my first novel Penelope and The Birthday Curse in the spirit of a Agatha Christie mystery. A guest at Penelope's birthday is murdered, a snow storm isolates everyone and the adults are clueless who did it. Penelope steps in finding clues and sleuthing. In the end she puts it together and....well, read the book.
A favorite show of mine is Death in Paradise. The murders take place on the island of St. Marie. As always there are suspects and clues, but who did. A Detective Inspector from the UK and local police must discover who did it?