Ah yes, the great Margaret Millar. I felt like a bit of a fiend simply reading this book in public. How freaky is that cover! I'm a huge Patricia Highsmith fan, but I'm believing more and more that Millar belongs in her class and is maybe even superior in some respects. Millar is less clinical. She seems to have some affection for her characters, though she is absolutely unsparing in the way she exposes their weaknesses and flaws. It gives a bit of warmth to her books that make them perhaps a richer read. Boy is she unsparing, especially towards women (another similarity to Highsmith). A smarter person than me with more time should dedicate at least a long article, if not a book on comparing the two authors and their works.
The Fiend is ostensibly the story of a mentally damaged individual, Charlie Gowen, who lives with his older brother. There was an incident with a child that happened in his past, sent him to a ward and made him the town pariah. Today, though, at least on the surface, he is more or less coping and the few people he does interact with consider him more or less "fixed", if they are even aware of his history. His brother, though, has basically sacrificed his life to take care of him and he is highly attuned to any potential weirdness or strayings. And Charlie is straying. He has noticed a particular little girl, Jessie a little daredevil, and is started to become obsessed with her safety. He wants to "protect" her. Millar draws out his pathology very gradually (as well as the details of his original crime), so you never really know how far he will go or the exact nature of what it is he will ultimately do. It's nerve-wracking! The question of whether he can exist in society is on the table and you do feel some sympathy for him.
Charlie's story is actually the center of a much richer plot, involving the little girl's parents and the two other families that are close to her: the childless couple of whom the wife is obsessed with Jessie and the bitter, misandrynist divorcée who is the mother to Jessie's best friend. It is in the portrayal of these people where we start to see the real human ugliness. It would be simplistic to pit the seemingly normal people against Charlie, but that isn't what Millar does here. Everybody gets their brain opened equally and revealed to the reader. Charlie's is just much more inconsistent and difficult to figure out. But they are all pretty messed up in one way or another.
I suspect that a professional psychologist would probably find some of the analysis of Charlie's mind possibly a bit dated or erroneous. There were some parts that seemed a bit facile (though a lot of those came from the perspective of a character, so it's hard to say if Millar was reflecting her own take or what she thought the character would think). There was also a small side development between the divorcee and her lawyer that seemed forced and unnecessary. But otherwise this is a pretty excellent book that keeps you hooked right to the end.