The book focuses on the experiences of the teenagers dealing with the invasion and the immediate aftermath, leaving the origin of the invaders shrouded in mystery. This ambiguity is likely intentional, contributing to the sense of uncertainty and fear that permeates the story.
Some clues are given:
* The invaders are technologically advanced: Their weapons and technology are far superior to anything the Australians have.
* They speak English: Although sometimes broken and with a strange accent, they are understood by the characters.
* They are hostile and ruthless: They act with aggression and little regard for civilian life.
However, no definitive information about their origin, culture, or motivation is ever provided. This leaves readers to speculate and draw their own conclusions about the invaders.