1st Theme - Standing up for what you think is right
One of the themes for this book is standing up for what you really think is right. In the story, Jen planned out a rally to protest against the government to set shadow children (third children) free. She really thought it was really necessary to do that. So, when it was time, she went on with her rally with 40 other people. Even though the rally failed and they all sadly died, they did what they thought they had to do. That's why Luke didn't go, he didn't think it was right to do it because he thought it wouldn't work, and it didn't.
2nd Theme - Survival
The second theme for this book is survival. Survival fits this book as a theme because to be a third child with the population law of only having 2 children per family is being reinforced, you have to be sneaky and careful of what you do to survive. Luke is very good at survival because he knew he had to stay in his attic and not go near windows. As with Jen, she always went near windows and she was seen by only Luke, luckily. When Luke did disobey the rules, though, he was still really careful. For example, when he went over the Jen's house, he was careful when he crossed his yard. Also, he made the right decision and to not go to the rally because he knew it wouldn't work.