This book is a prequel, jumping back from where we landed at the end of Wool to the very beginnings of the silo system. It's broken up into three distinct "books," each one shifting perspective to tell a slightly different part of the story.

At first, we meet a well-meaning yet mealymouthed congressman named Donald. Years later, we meet Troy, the bewildered manager of Silo 1. These two perspectives bounce back and forth, each one revealing a little more of the whole picture until it all comes together with a horrifying clarity. From there, we dive deeper into the silos. Silo 1. Silo 18. Silo 17. Each one has its main character and goes through ups and downs, always with the characteristic grimness I expect from this series.

Finally, at the end of the book, we converge on the present moment and learn a little bit about what happened to Juliette after she left Silo 18. It's a tense setup for what kind of reckoning to anticipate in the next book. And shockingly, even with this whole book of backstory, some worldbuilding mysteries still remain to be revealed.

Overall, this book was interesting and I'll definitely read the next one.