We follow two girls, more than 1000 years apart. At least, that is stated in the text but is never clear from the way the world changed. It could just as easily have been 100 years apart. Or fifty. My other complaint is that there are some trials in this book, that were just not interesting. I didn't feel afraid for the characters involved in the trial and I found the trials to be confusing. I couldn't picture them clearly in my head.
If you like Sarah J Maas her books (at least her Throne of Glass series), you will probably like this one as well. I have negative things to say about both, but I enjoy too much to give a negative review.