I finally got around to reading 'Magpie Murders' last week, and the central puzzle is seriously clever. The book is structured as a novel-within-a-novel. The main mystery we, the reader, are trying to solve is the death of the author, Alan Conway. He's found dead at his home just after delivering the manuscript for his latest Atticus Pünd mystery. His editor, Susan Ryeland, believes his death wasn't a suicide and that the clues are hidden inside the unfinished manuscript he left behind.
So you're essentially solving two layered mysteries. There's the classic whodunit in Conway's book, where Atticus Pünd investigates a murder in a 1950s English village. But the real, modern-day mystery is what Conway was trying to communicate through that story and who wanted him dead. The manuscript is missing its final chapter, so Susan has to piece together the ending from Conway's life and the fictional clues. It's a bit meta, but that's what makes it fun—you're reading a detective story while also watching a character read a detective story to find answers.
The whole thing hinges on anagrams and literary references. Conway was apparently obsessed with them, and Susan starts to see parallels between the fictional characters and real people in Conway's circle. It becomes a sort of treasure hunt through both texts. Honestly, I got so invested in the Atticus Pünd story that I was almost annoyed when it cut back to the modern timeline, but that's kind of the point—you get sucked in just like Susan does.