In a vacuum, this is a very good holocaust book--above-average for the genre in that it shows a less-well-known camp and the women who were the victims of medical experimentation. The one thing that weakens it is the recurring reference to Maddie--a reminder that this is connected to Code Name Verity, that it's the same author, that this is following closely on the heels of an amazing, complex, twisting novel. In other words, it's a strong book that spends a lot of time reminding me how much more it could have been. 
 I also never connected with Rose, really--for all the many things she did, she never stopped having a certain helplessness about her, a chronic going-through-the-motions even though she did plenty. This is probably realistic to the prisoner experience, but even before that there was something about her that seemed so passive. I just never liked her much.