Ten years ago, Spenser helped a teenage girl named Mattie Sullivan find her mother's killer and take down an infamous Southie crime boss. Now Mattie dreams of being an investigator herself. But like her mentor and boss, Mattie has a knack for asking the right questions of the wrong people. Soon Spenser and Mattie find ties between the exploitation of dozens of other girls from working class families to an eccentric billionaire and his sadistic henchwoman with a mansion on Commonwealth Avenue. Spenser and trusted ally Hawk must again watch out for Mattie as she unravels a massive sex-trafficking ring that will take them from Boston to Boca Raton to the Bahamas, crossing paths with local toughs, a highly-trained security company, and an old enemy of Spenser's—the Gray Man—for a final epic showdown.