The Woods (symbol)
At the beginning of the book, Luke mourns the loss of the woods, which are being torn down to create a housing complex for the wealthy. Because these woods are the only place he can go to outdoors, they have become a symbol of freedom for him.
The Toy Train (symbol)
Early in the novel, Luke plays with a toy train that was a hand-me-down from his brothers. He knocks it over in frustration, thinking that he's too old to play with such children's toys. Knocking it over signifies Luke's discontent with his lot in life and his determination to leave his childhood behind.
Fake Identification (symbol)
One of the few ways that Shadow Children are able to live a normal life is by obtaining fake IDs and taking on new identities. However, Jen argues that this is just another way of hiding since the Shadow Children still have to lie about who they really are and live in fear of anyone finding out their true identities. Therefore, the fake IDs become an ironic symbol of secrecy and hiding.
Chips and Soda (symbol)
Junk food is technically illegal because the Government wants to make sure that the population has access to healthy foods. However, Barons are still able to access such luxuries, and Jen offers some of her junk food to Luke. Junk food, which is delicious but void of any real value, is symbolic of the indulgence nature of the Barons.
Jen as Eve (allegory)
In the Bible, God makes Eve in order to give Adam (the first man) a companion. However, Eve eats the apple of knowledge after being tempted by the Devil, and both she and Adam are cast out of Eden.
Like Eve, Jen is the first female whom Luke has ever met, apart from his mother. Jen introduces Luke to a number of new things: junk food, the internet, friendship, and questioning authority, to name just a few. She encourages him to push back against his parent's demands for obedience and hiding. Eventually, she dies standing up to authority, just as Eve was punished for denying God's authority.
This is a rather limited and traditional reading of the story of Adam and Eve, though Haddix seems to draw on it for creating the defiant and ultimately tragic figure of Jen.
