The irony of the chase
We aren't exactly told why Ellie is flying through space, except that we know she has hijacked the space pod to go back home to her parents on earth. It is ironic that a 12 year old girl is being chased by a powerful man like Mal Gordon and his forces. Why should a young girl matter in the grand scheme of things? It is because of her love for family and freedom, and because her mind is a powerful tool.
Mika's anger
Ironically, Ellie's welcome home party isn't very fun. Her parents are mostly stunned and confused, and a little concerned for what Ellie's survival might mean for them in the post-apocalypse where it is hard to provide for even the three of them. Mika's anger is the ultimate irony, because he isn't even really mad at Ellie—he is sad for their time apart, and he is overwhelmed by relief.
The irony of the wall
The wall is ironic because it separates society from nature. It's all fun and games until they literally cannot leave anymore. Ironically, they can still travel to and from space (the rich people can anyway), but they cannot go home to the green habitat humans are designed for, because of this 50 foot wall that sits along the perimeter.
The irony of misinformation
Mal Gordon tells Ellie's parents that she is dead, and then when she turns up again, he captures her again and tells her brother that she is dead. He also lies, saying the animals of the earth have been eliminated by a toxic yellow smoke, but ironically, when Ellie and Mika escape London, they find that even that has been a lie. When there is some misinformation, who knows where the truth begins?
The irony of heroism
Some people still believe only boys can be heroes, but here we see a girl, and a young girl at that, only 12, having to live in a world that is horrible and scary, but she survives. Not only that, she manages to return to London and rescue her little brother. That is a lot of heroism for a girl just over a decade old. It seems that anyone could be a hero, given that they trust their emotions and instincts, and that they operate based on love for their community.
