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A good detective story has a recognizable rhythm. The plot might have unexpected twists and the characters can surprise you. But there are certain structures and tropes that recur

through much of the crime fiction from the first half of the 20th century. Some of

them have been parodied to the point of cliche, such as the old The Butler did its solution.

But they are usually there nonetheless, providing the author with some creative constraints and the reader with a frame of reference.

Even if you aren't a big mystery reader, these founding principles of the genre are so familiar

that I expect you'd still be able to name a few.

Nothing supernatural, no secret twins, no springing clues or suspects on the reader in the final chapter. The list goes on.

But how did these presets come to be woven through the books from the golden age of detective fiction between the two world wars? And what happens when you break the rules?

Welcome to She Dunnet. I'm Caroline Crampton. My obsession with what is and isn't allowed in a detective story began with A. A. Milne.

Although he is best known now for creating the 100 acre wood in its residence, Winnie the Pooh, Piglet, Eor, and so on.

Alan Alexander Milne was also a journalist, playwright, and novelist, publishing work both before and after the First World War.

He also had a consuming passion for detective stories, and in 1922 published one of his very own, The Red House Mystery, in which the host's long-lost brother

is found shot dead during a country house party, and two of the guests turned to sloothing

to solve the puzzle. It was a great success being reprinted many times and is still read today.

Four years later he wrote a new introduction for the 1926 edition and in it Milne set out his own curious preferences about what a detective story can and can't be.

He wanted his whodunit's written in plain English,

without the intrusion of a romance plot, starring an amateur detective who works just with logic and reasoning

...