From the visit, Scarlet learns that her father (who she always thought was a deadbeat) is actually an infamous psychopathic mass murderer, who went to jail when she was only two years old. In order to escape intense media scrutiny, her mother took her and fled, assuming a new identity. Now, the man is dying and he has promised to reveal the identity and final whereabouts of hitherto unknown victims. But only if he can see his daughter.
Once Scarlet gets over the shock of finding out her true identity, she's repulsed by the idea of meeting such a man, even if he is her biological father. The FBI, however, are eager to get her to do it. There are dozens of cases that they suspect are tied to the man and solving even a few of those cases would make a world of difference to the victims' families. Conflicted between the desire to maintain some privacy and a feeling of obligation to the victims, she goes and meets the monster.
While setting up this implausible scenario takes some work, once McLaughlin gets us through the prerequisites, the rest of the story basically writes itself. It has all of the seductive yuck factor of Silence of the Lambs and it's a page turner from beginning to end. It's precisely that appeal that turns out to be the point in the end. A steady theme throughout is exploring why people are so obsessed with stories like this. Do we just like macabre things or are there people who harbor dark fantasies that they live out through histories like these? And why draws women to men who murder remorselessly?
In addition to such deep and dark ruminations, there's some attempt to work in a romance, but this isn't a story one gets feeling sexy about. Lots of drug references may make some readers more uncomfortable than the grisly subject matter. But overall, this is great entertainment, which is probably proving the author's underlying point.