I love the fact that in this series we see the investigation step by step.
I liked Allison, she was 27 and the only female detective with something to prove since she's young, female and new to homicide, so despite the fact that no-one believes her about a serial killer she works on it along with the hero, FBI agent Mark who first caught wind of this killer ten years ago.
Mark is 43 and married to the job and divorced. He has too much of drive for the job and no time for other things. We see their age play out, he is the more experienced agent and he does tell her that sometimes but I found no inequality. He looks at her and seems someone who is not jaded yet and he does want that.
His bad childhood was alluded to but never expanded on which I didn't like. He doesn't want to act on his attraction for Allison but she does and he tries to back away. I liked how Allison tells him that he will turn into a robot at the pace he works & liked the end when he comes to work for the Delphi Center.
One other thing bothered me, she seemed reckless sometimes because of the pressure to prove herself.
Looking forward to the next book about Kelsey and Gage.