As before, the parallels (Marla's brother last book, her evil twin in this one) serve as effective reflections for just how relatively not-horrible Marla is.
The book comes with author's notes attached (at marlamason.net) and I found them salubrious. There are places where I was insufficiently suspicious of Marla's narration. I'd rather cheat than miss the clues entirely. (Although I read the notes after the book, not chapter-by-chapter interspersed.)