(I got an ARC of this book courtesy of Edelweiss. The book being published by now, a few things may have changed, compared to the version I read.)
I can't say I hated this novel, but it didn't leave me with a strong impression either. I expected more darkness from Kit, more moral ambiguity; instead, I found a lot of little things that constantly challenged my suspension of disbelief.
I think the main issue for me was a pitfall a lot of stories about serial killers have to avoid: how to make the killer really dangerous, while also giving him/her flaws that would allow other people to catch him/her? Because, obviously, if the murderer's so perfect nobody can ever uncover his/her true identity, there's no challenge, no conflict, in terms of both plot and character development. This is where the story failed for me: Kit is "the Perfect Killer", but the way she acts in the novel, it's a wonder she wasn't caught before. She befriends a Scotland Yard detective and almost immediately gives out information the police's not supposed to know. She kills in her own school, and sets it up to make herself the only witness. She inserts herself into the investigation, goes back to the crime scenes, even lets one victim go free. She takes some care not to leave prints by using gloves all the time and not resorting to weapons that could be found... but she's not too savvy when it comes to the more advanced forensic techniques.
Unbelievable, therefore, was the police's incompetence. Everybody in London seems to know where the "Dear Killer"'s mailbox is, but the police never found any lead. Kit's signature are letters from the very people who asked her to kill, containing extremely valuable information about them and the victims; 50 murders later, how come none of those has ever led to a clue, how come the police hasn't managed to get a confession allowing them to find the mailbox, if only by striking a bargain with a guilt-ridden "customer"? Also, Alex shouldn't ever have allowed Kit on a crime scene, nor talked about the investigation. This works in Dexter because he's already a member of the police force—but even Dexter's presence on some scenes is questioned by his colleagues, when there aren't any blood splatters to check, so if Dex can't be there without rising suspicion, how can Kit, the teenager, whose only link with the police is the detective her mother once brought home for dinner?
Then, there's the ambiguity of Kit's position regarding her jobs. Is she really a serial killer, or a hired killer? Does she really off people because of some urges, or is she merely doing what her mother taught her, is she what she was brought up to be? Is her moral nihilism truly that, and does she even know where she stands? My qualms with those questions is that they were never really examined, and Kit's actions and thoughts felt too random to really play a part in what could've been serious introspection. Once she says there's no right nor wrong, and then she seems to believe she kills for justice, but the killing jobs she chooses to carry can't be justified this way (one guy writes that he wants her to kill his fiancée, because he was involved in a hit-and-run, and now she wants him to confess to the police... so Kit kills the woman, no questions asked, when clearly "justice" would've been to get rid of the guy who had already taken a life). I would've find it more believable if she had questioned her choices on that level; she starts doing it with the one victim she lets go, but considering who her last victim is at the end, it might as well never have happened.
Kit's relationship with her mother was probably what kept me reading: extremely unhealthy, riddled with her mom's own madness. Mrs. Ward: a women who had married a certain man only so that she could be left alone, who had transferred her urges to kill onto her daughter, and basically shaped a kid into a monster. Maybe the idea of a teenage killer was a bit stretched, but it didn't matter, because there was a reason behind it, and it was something I could go with (children find their first examples in their parents: what if the parents themselves are dysfunctional to the extreme?) Like a trainwreck, it was something I couldn't help but watch, even though it was deeply unsettling, and just like with Kit's moments of doubts about her killings, there was something interesting underneath it all, some deep questions to be asked; however, it wasn't carried far enough in my opinion to shine through. In general, I found Kit's thoughts and observations remained too much on the surface level, and what could've been character growth (acceptance, finding herself through her killings, different moral choices, whatever) only started happening, yet never went there.