Grant McAllister, an author of crime fiction and professor of mathematics, once sat down and worked out the rules of murder. That was thirty years ago and now he's living a life of seclusion on a quiet Mediterranean island - until Julia Hart, a sharp, ambitious editor, knocks on his door. His early work is being republished and together the two of them must revisit those old stories: an author, hiding from his past, and an editor, keen to understand it. But as she reads, Julia is unsettled to realise that there are things in the stories that don't make sense. Intricate clues that seem to reference a real murder, one that's remained unsolved for thirty years. If Julia wants answers, she must triumph in a battle of wits with a dangerously clever adversary. But she must tread carefully: she knows there's a mystery, but she doesn't yet realise there's already been a murder.