Rhyme's cousin has been arrested for murder. The evidence clearly shows he did it, but Rhyme agrees to check things out. It turns out that the cousin along with other people has been wrongly convicted because the true killer knows every single detail about the lives of the victims he kills and the men he sets up to take the fall for those crimes. This allows him to get close to the victims under false pretenses, murder or rape, and escape safely. And then he sets up others to take the fall for his crimes, planting incontrovertible evidence Rhyme, Sachs and the rest of the team have to find out who at the huge, ominous data mining company is getting access to this information. Meanwhile the villain--known only by a number to us--realizes he's being pursued and turns his knowledge of data and information into a weapon. Oh, and lest things seem too delicate, he also gets information through good old-fashioned murder and torture too.