Space pods
The space pod pursuits are epic, and they are also symbolic. They symbolize Ellie's mastery of futuristic technology, a skill her parents don't really share. She has bravery and intuition, and she correctly navigates obstacles. This means that space pods are also a symbol for her "making her own way" in life.
Mal Gordon as an archetype
Mal name literally means "bad" in Latin. It's no surprise that the novel uses his character as a tangible picture of evil. He uses his power to exploit the weak and powerless, to add to his own control. As a controlling person, he often lies, manipulating people by giving them false beliefs, and he tries to use Ellie's psychic powers for himself.
Mika as a symbol for family
Mika is Ellie's brother, but in the ending of the novel, we see that Ellie has accepted a role as care-taker in Mika's safety. Having experience in tough situations, she has become qualified to help and support her little brother better than their parents. Together, they serve as a picture of family as they continue to survive together.
The yellow gas
The yellow gas is a symbol for humans damaging nature, because the gas allegedly exists to kill all animal life outside of London's humans. But, actually, the gas isn't even real. It is a ploy designed to keep Londoners behind the epic wall that exists around the perimeter of the city. The gas is a symbol for death and for the confusion caused by misinformation.
The wall
The wall is an ultimate symbol. The wall represents strong boundaries and commonly held assumptions that limit a community. In this book, it represents being cut off from the outside world, and the emotional feelings of loneliness, detachment, and the rift that Ellie feels between her and nature. She wants to be somewhere green and open, not grey and closed off.
