I often speculate, while reading books, about what's going on with the author and/or characters. A good author can write a very convincing character with a severe anxiety disorder, say, without once using the word anxiety -- I wouldn't be too surprised to find out that in the course of writing the book, the author interviewed people who had or worked with people with an anxiety disorder, read forums devoted to these disorders, read the diagnostic criteria, etc. Recently, while reading Michael Lewis' _The Big Short_, I became convinced that at least one and probably more than one of the people being described could be diagnosed with ASD and indeed, halfway through the book, Lewis reveals that one of them got an Aspie diagnosis after their kid was diagnosed. It was handled in a positive way (by the family, the people they were working with and by Lewis as the author), but I was additionally happy because I rarely get that kind of "answer key".
Reading Harkness, it seems clear that the "creatures" (supernaturals or supes, in my terminology) are written to capture some ideas about mental illness -- the daemons, in particular, are said in this modern age of declining powers as having less genius and more mental illness, and their behavior includes a raft of possible symptoms suggesting anything from ADHD to bipolar to schizophrenia or other. And to be utterly clear, they're the _nicer_ people in the book.
However, the protagonists, Diana Bishop and Michael Clairmont or de Clermont or whatever, have a relationship that keeps making me want to send them both off for counseling. Separately. And that makes me wonder whether I really want to keep reading at all.
Also, kissing someone "in the French manner"? Who thinks like that? Writes like that, whatever.