In Tana French's psychological thriller, "The Likeness," Irish detective Cassie Maddox is shocked to learn that a woman who was found stabbed to death bears an uncanny resemblance to her. Even more startling, the deceased had been using an alias that Cassie and her boss, Frank Mackey, had invented for Cassie when she was working undercover. Years earlier, Cassie had posed as Lexie Madison in order to infiltrate a drug ring in University College, Dublin. Now, she has a position in Domestic Violence, having had her fill of both undercover and the Murder Squad. The question remains: How had the victim come by Cassie's alias and why was she using it at the time of her death? In what at first seems to be a harebrained scheme, Mackey convinces Cassie to pose as Lexie (who, the story would go, recovered from her wounds and didn't die after all) and return to her former life in order to learn the identity of Lexie's murderer. Cassie is the brash first person narrator, a risk-taker who believes that she can talk her way into and out of any situation. Although her boyfriend and fellow-detective, Sam O'Neill, is opposed to Cassie's potentially dangerous new assignment, she is jazzed as the opportunity to resume the exciting life of an undercover detective. She misses the delicate balancing act of assuming someone else's persona. This will prove to be a harrowing case that will test Cassie's acting ability, nerve, objectivity, and professional judgment. French has an evocative writing style that richly evokes both setting and character. The author's biting and sardonic humor adds flavor to this complex novel. "The Likeness" is more than a murder mystery. It is also an engrossing exploration of the nature of identity. What makes each of us unique? Which is the deeper connection--the ties of blood relatives or those of close friends? French also deals with the nature of reality and illusion and the many ways in which men and women deal with serious emotional trauma. During this assignment, Cassie will suffer from the stress of living a double life. On the one hand, she is Lexie Madison, a student who lives in close quarters with four housemates, one of whom may have been her killer. On the other hand, she is a cop who reports to Frank and Sam, offering her perspective on what may have happened to Lexie. Unfortunately, Cassie becomes so consumed with her alter ego that she begins to forget where she ends and Lexie begins; the two become inextricably intertwined. The book's flaws include a plot that becomes increasingly implausible as the story progresses. In addition, French goes into too much detail in her analysis of Cassie's past, behavioral quirks, and innermost thoughts. What keeps the book moving is the intriguing and unconventional relationship between the five postgrads who dwell in Whitethorn House: Lexie, Daniel March, Rafe Hyland, Abby Stone, and Justin Mannering. To one degree or another, they are all running from the past. Either have no parents or they are estranged from them. Yet there is something vaguely unhealthy, if not bizarre, about an almost pathological clannishness that discourages outsiders from invading their magic circle. "The Likeness" is suspenseful and absorbing, but it would have been even more effective had a judicious editor trimmed the manuscript, eliminating some of the repetition and extraneous information that occasionally slows down the proceedings.