Writing historical fiction is uniquely challenging, not only because of the need to research countless details but because it can be so difficult to truly enter into the mind of someone whose view of the world is, in some ways, quite alien to our own. When the narrative is written in the first person, the difficulty is compounded. The narrator must never use a modern turn of phrase.
In The Alienist, Caleb Carr seems to have done a fine job researching the details of life in New York in 1896. But his narrative voice is not flawless. The narrator, purportedly writing 20 years after the fact, in 1919, at one point observes two other characters, a man and a woman who may possibly be romantically linked, and reports their interaction in these words: “…the strange chemistry between them…”.
I’m pretty sure that’s an entirely modern use of the word “chemistry.” Certainly chemistry itself was well known in 1919, perhaps even better by the average person than today. But “chemistry” was not used as a metaphor to describe subtle personal interactions.
It’s not a bad story, even so. Very sensationalized, and some of the criminology is also suspiciously modern, but I’d have to do research to be certain.