First of all, here's what's implied: Our home planet has been destroyed due to an extraordinary, yet unspecified act of violence.
Second, some background: A handful of humans who survived this disaster fled to Green Sky, a planet of low gravity whose surface is covered by trees so large that could easily dwarf the mighty redwoods. It is here, among the treetops, that these survivors make their homes and create a new life based on the principles of peace, love, and happiness and put all their faith in a secrative and exclusive group of leaders who call themselves the Ol'Zhaan. Fearing that history will repeat itself, these leaders make all forms of voilence (and even the mention of it), as well as all expressions of strong emotions, illegal. They erase their tragic past from the history books, and it is eventually forgotton. Anyone who opposes this way of thinking or who wishes the general public to know the truth about their past is quickly disposed of, imprisoned in an underground prison that is covered by an elaborate and magical root system. To explain the disappearances of these, Ol'Zhaan tell the general public that the missing must have been taken by the terrible, flesh-eating monsters who live beneath the root.
Eventually, a Pleasantville-like community of cluless, peace-loving flower children-like citizens is established. The people are happy in their ignorance and in their naive (and almost moronic) trust in their leaders. The only real threat they know if is the (false) threat from below.
But escape from below the root is impossible.
Or is it?
Flash forward a few thousand generations: The original few human prisoners below the root has grown into a large community who call themselves the Erdlings. Here, the people are experienceing the worst famine in their history--and signs point to things only getting worse. People are desperate. So when 8-year-old Teera learns her beloved pet will soon be killed and eaten, she runs away... as far away as she can. Soon she is lost in a system of abandon mining tunnles. It is here where Teera finds an opening in the root large enough for a child of her size to squeeze through. She escapes into the forest.
Meanwhile, in the treetop community, things have been going downhill. The general clueless innocence of the Kindar is costing them dearly, although only the Ol'Zhaan know the extent of this. The powers of Spirit (not unlike the famed Force) that were once so common have become nothing more than myth. Wanting to get to the bottom of this disappearance of Spirit, the Ol'Zhaan send two young apprentices on a quest to solve this mystery. This quest leads them to the forest floor.
It is here they discover Teera.
Thinking her to at first be a Fallen (an infant who fell from the treetops and was rescued by those rebels imprisoned under the root), they take her home and she becomes part of their family.
Then they learn the truth about Teera.
And the truth about those who live below the root.
And that there ARE no monsters... Or, at least, the monsters aren't what everyone has been led to believe (in fact, said monsters have been living among them for generations)
And they come to the conclusion that the people below the root must be freed. And that the people of Green Sky communitues must be told the less-than-desirable truth about their past. Even if it means they will have to face up to the terrible feeling and emotions the truth will bring. Even if it means the end of the Ol'Zhaan.
But there are those in the Ol'Zhaan who will stop at notning to prevent the truth from being exposed. Even if it means resorting to the violent ways the order swore to protect against.