I have to give French her utterly ludicrous core concept: two people who are almost exact doppelgängers, not related. Yea, pull my other leg. And, I couldn't care less in the end. It did bother me in the beginning, and made me worry that the sophomore effort was not going to live up the freshman effort (and what an effort that was). There is nothing to fear here.
Once again, she pulls all your emotions out of your stomach, tosses them around like soccer balls for 500 pages, and then lets them fly away like little birdies on the last page That's how spent you feel when you're done. I don't really know how she does her magic - action that flows from page to page and from one plot device to the next, seamlessly. And especially at the end, never telling you the whole story so that you absolutely must read between the lines, and absolutely must remember plot devices from 200 pages back. When you "get it", you literally gasp. That is stellar writing.
And there's more. In between all the plot devices are little descriptive passages that take your breath away. In this book, descriptions of tiny country lanes in the dark, of long and sweet hot summer afternoons, of the kind of house that isn't lived in anymore and can only be seen in a museum setting. I'm convinced she's had some experience writing poetry (and I'd like to read some of it).
After reading two of her books, I think it's safe to say that I'm considering her the best mystery series writer I've ever read. Yup.