Tana French was an actor in her thirties when she sat down to write about a mystery that took the lives of two children, which became the global blockbuster “In the Woods.” With her subsequent books about the Dublin Murder Squad, French became known as “the queen of Irish crime fiction”—despite having been born in the United States. French’s latest book, “The Witch Elm,” departs from her line of police procedurals: the narrator is a civilian, a happy-go-lucky young man named Toby whose life is turned upside down when he is attacked during a burglary. Although the book involves a murder, “The core story arc is not the murder and the solution,” French tells Alexandra Schwartz. “The core story arc is Toby going from this golden boy [with] his happy life to somebody who’s had that shattered. . . . Where will this crisis take him?” Though known as a literary mystery writer, French acknowledges that some of her fans have found the plot frustrating. “If you’re coming to this book expecting a straight-up crime novel . . . you are going to be a hundred pages in [asking], ‘Where’s my murder?’ ”