Mac is down with the flu when his best friend Detective Billy Staples sends him a text message that is a plea for help. But Mac is too sick to move. Karin goes instead, meeting Billy at midnight on a dark, deserted Brooklyn street where Billy has been called out on a case.
After easing Billy out of a flashback signaling his descent into post-traumatic stress disorder (PTSD), Karin discovers that there are not one but two crime scenes. An eleven-year-old girl, Abby, has barely survived an encounter with a hit and run driver. One block away, a prostitute has been found murdered—with a knife left embedded between her breasts, the signature of "The Working Girl Killer" who terrorized Manhattan for two years before arriving in Brooklyn a year ago. Billy has been one of the detectives working that case.
The next day, another brutal murder is discovered nearby. A media firestorm ignites in the quiet neighborhood where Karin and Mac have settled down with their young son Ben. Karin, distraught over her recent miscarriage of a baby girl, throws herself into the case with Billy as they seek to understand whether the two crimes are connected or just a nightmarish coincidence. Abby is the link, and the only potential witness, but once she emerges from a medically induced coma she can't, or won't, talk. Having learned about PTSD from Billy's worsening condition, Karin begins to suspect that Abby may also be suffering from the disorder as a result, perhaps, of having witnessed her parents' murders.
But the truth is not that simple.
As Karin, Mac and Billy dig deeper beneath the surface of the crimes, shadows of suspicion appear where least expected. And Karin, with an unexpectedly acquired twelve-year-old adopted daughter, Dathi, suddenly expanding and enriching her family, finds herself in the fight of her life to save two preteen girls—Abby and Dathi—from a treacherous web that had spun itself unseen into a fabric of international human trafficking that must now be unraveled before more innocent lives are destroyed.