As a journalist, Cate Holahan ’02 covered some dark stories, like the Bernie Madoff scandal. Today, she uses what she learned to write domestic psychological thrillers. Karma always comes for her characters, but there are no perfect villains, and no one emerges a complete hero. In her fifth and latest book, “Her Three Lives,” Holahan probes the way security technology can twist a mind pushed to the edge by violence and paranoia.