Marble Hall Murders: A Novel - Anthony Horowitz

Murder links past and present once again in this mind-boggling metafictional mystery from Anthony Horowitz—another tribute to the golden age of Agatha Christie featuring detective Atticus Pund and editor Susan Ryland, stars of the New York Times bestsellers Magpie Murders and Moonflower Murders.
Editor Susan Ryeland has left her Greek island, her hotel, and her Greek boyfriend Andreas in search of a new life back in England.
Freelancing for Causton Books, she's working on the manuscript of a novel, Pund's Last Case, by a young author named Eliot Crace, a continuation of the popular Alan Conway series. Susan is surprised to learn that Eliot is the grandson of legendary children's author Marian Crace, who died some fifteen years ago—murdered, Elliot insists, by poison.
As Susan begins to read the manuscript's opening chapters, the skeptical editor is relieved to find that Pund's Last Case is actually very good. Set in the South of France, it revolves around the mysterious death of Lady Margaret Chalfont, who, though mortally ill, is poisoned—perhaps by a member of her own family. But who did it? And why?
The deeper Susan reads, the more it becomes clear that the clues leading to the truth of Marian Crace's death are hidden within this Atticus Pund mystery.
While Eliot's accusation becomes more plausible, his behavior grows increasingly erratic.. Then he is suddenly killed in a hit-and-run accident, and Susan finds herself under police scrutiny as a suspect in his killing.
Three mysterious deaths. Multiple motives and possible murderers. If Susan doesn't solve the mystery of Pund's Last Case, she may well be the next victim.