All of the twin stuff is amazing, and I was not surprised to read that Overton has an identical twin because she hits the Abby/Lily relationship out of the park. Honestly, two stars are for the twin relationship with an extra star for Abby being a badass, because the rest of the story did not hang together as much as I hoped that it would. 
 I predicted most of the story before it unraveled and the part toward the end that was a surprise was mostly glossed over after it happened. I know few children but Sky must be an impossibility at her age and in that situation (and I do understand not wanting to rewrite Room but in this type of story I need more than "we went to therapy and we dealt with X, Y, and Z fears"), and Lily was not much better in her therapy scenes. I was more interested in Abby and Eve than I was in Lily and Sky because there was more emotion and rawness to the writing with those characters and I wonder why (although I have my guesses). Basically, I wanted more from the novel than it delivered.