Just finished "Partners In Crime" by Agatha Christie. This was her 11th book, and was originally published in 1929.
Although this book has an overall "plot", it's essentially a short story collection featuring "Tommy and Tuppence", who first appeared in Christie's 2nd novel, "The Secret Adversary". In this book they are running a detective agency, and each chapter (or sometimes 2 or 3 chapters) describes one of the cases they tackle.
The interesting twist in the book is that they are themselves big fans of detective fiction, and in each case they try to adopt the methods and quirks of a famous (famous at the time, that is - most of them are now long-forgotten to most modern readers) fictional detective. Thus in the first story they adopt the methods of R. Auston Freeman's forensic investigator Dr Thorndyke; in a later one they try to solve the crime in the manner of G.K. Chesterton's Father Brown, and so on. Amusingly, in the final story they adopt the methods of Christie's own Hercule Poirot, and poke fun at Poirot, and specifically at Christie's book of the previous year, "The Big Four"
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A fun book. Well worth reading.