Exclusive: Melissa G. Moore and Annaleigh Ashford discuss Happy Face and what it's like to be a monster's daughter.

Archie Sheridan, a police detective, spent years chasing one of the most deranged and vicious serial killers to ever appear in the pages of a book, the beautiful and completely insane Gretchen Lowell.

And there is no shortage of experts offering opinions on the various characteristics of serial killers--their personalities, motivations, methods of operation, and crime-scene behaviors.