“Genius” is a loaded term. Its application usually says more about the person making the judgment than it does about the genius in question. In The Guardian, Sophie Hannah argues that the term isn’t used enough to describe one writer in particular: Agatha Christie. You could also read Daniel Friedman on the terrible secret of all crime fiction.
You may have heard that J.K. Rowling published a crime novel last year under the pen name Robert Galbraith. According to her alter ego’s website, Rowling will publish another novel as Galbraith, one featuring (again) the private investigator Cormoran Strike. (If you missed it, you should definitely read Elizabeth Minkel’s recent piece on Ron/Hermione and authorial regrets.)