“The Secret Place” (Viking), by Tana French Tana French is irrefutably one of the best crime fiction writers out there. Her latest, “The Secret Place,” is a mesmerizing story set in a girls’ boarding school in Dublin. The murder of Chris Harper, a student at the neighboring boys’ school, happened about a year ago and the case is cold, until Detective Stephen Moran, last seen in 2010’s “Faithful Place,” receives a visit by Frank Mackey’s daughter Holly (also of “Faithful Place”). Holly is now 16 and a student at St. Kilda’s. She brings Stephen a photo of Chris, captioned in ransom-letter text, “I know who killed him.” The photo had been posted on a bulletin board called the Secret Place, a safe space meant for students to anonymously unburden themselves of things they weren’t comfortable sharing with friends and family. (French has said the inspiration for the Secret Place came from the popular website PostSecret.com.) Moran teams up with Detective Antoinette Conway, a marvelous addition to French’s stable of Murder Squad characters. Conway is razor sharp in both mind and tongue, and the platonic chemistry that develops with Moran is pure enjoyment. Together they spend a day at St. Kilda’s questioning two groups of girls: Holly’s gang and their rivals, each bent on framing the others not only for what happened to Chris but also any kind of school infraction that might get them expelled. Interspersed between the present-day investigation are flashbacks to the months leading up to Chris’ murder, literally counting down how many months and weeks he has left to live. It’s this back and forth between timelines that makes “The Secret Place” dizzyingly addictive, with each segment revealing a small clue to what happened the night Chris died. Slightly less compelling are the portrayals of the eight girls Moran and Conway interview; at times it seems as though none of the girls understands the gravity of the situation, which is as frustrating for readers as it is for the detectives. This does not, however, undermine the weight of the story, the complex bonds of friendship particular to teenage girls, which French nails to an almost painful degree. Don’t miss this one.