The title of Greer Hendricks and Sarah Pekkanen’s suspenseful new psychological thriller is comforting . . . and sinister: “You are Not Alone.” The first-person protagonist is Shay Miller. She feels herself to be alone. Then she meets strangers who invite her into their exclusive gathering of young women. The group includes the sophisticated Moore sisters, who not only show her how to dress and act, but begin to make her uneasy. There’s something odd going on with them, though neither Shay nor the reader knows yet what it is. The irony is that Shay may have been better off alone, without the sisters in her life. The story begins innocently enough. Shay is sharing her New York City apartment with her former boyfriend and his new lady love. Not good, and Shay announced she’s getting out, and also looking for a new job in the city – she’s been downsized. Meanwhile, as she’s done all her life, she takes refuge and pleasure in her longstanding passion for collecting data and recording them