As one of the characters, B.J. Voisard, might describe it, this story is exactly like the quest for the grail, except it takes place in late 19th century America instead of medieval England, and instead of a grail there’s a mysterious woman with an unknown past who can’t speak, and instead of valiant knights there are a Chinese migrant, a suffragette, and an escapee from an insane asylum on quests to help her. Otherwise, it’s the exact same story.
The book is rich in detail and meticulously researched. The SF elements are more of an open question and it isn’t heavy on plot. The writing is excellent but the characters, quirky and memorable, make the book, particularly for me, the aforementioned B.J. Voisard. If you don’t find them engaging, this book really isn’t for you.