This story is all about the question of how and why an alien species might divide a planet so that one half remained in its natural state while the other half was terraformed. With help from scientists and her own imagination Czerneda pulls together threads of cryogenic colony ships, strange worlds, artificial intelligence, and alien minds so different from ours that every interaction is a puzzle. Even the human civilization of New Earth, the first and only known settlement of Original Earth, has some unexpected aspects. The characters and plot tend to take a backseat to the unique and strange possibilities of the universe in this speculative sci-fi story.

In a distant future colonists travelled over one hundred years in a sleeper ship to New Earth. As planned they sent back a message to say they arrived safely but there was no answer so decided human expansion was up to them and sent out six sleeper ships of their own. Disaster, in the form of a solar storm, forced them to launch the sleeper ships prematurely and ultimately destroyed their own satellites and stations killing thousands. In response they swore "Never Again" and developed technology similar to that of the movie Avatar in which those working in space transfer their minds to a replica of themselves called an Epitome so they can remain safely on New Earth. While they waited to hear back from any surviving sleeper ships New Earth was discovered by an advanced alien race known as the Kmet. The Kmet taught themselves English from our transmissions but communication is still barely possible. We understand only a few things. The Kmet demanded a single human representative for communication now known as the Arbiter. They demanded that humans live on the planet but not in space stations. They agreed to transport human cargo ships through the paired portals they live in that connect Kmeth space and to trade some tech, though not the portals because humans could only be in one place. Obviously, that last stipulation could be a problem and it has now been two hundred and six years since the sleeper ships left and a probe returns with the  message that one of the ships has landed on a new world. How will the Kmet respond?

On a distant colony of New Earth they're dealing with their own bazaar alien situation. The world is bisected by zone that tries to destroy any matter that tries to cross from one side to the other. Those who risk their lives to learn how to navigate the zone are highly valued for the specimens they bring back for study. The travelers are fairly certain the aliens who created the zone actually live under it but have never seen one and have no idea if they know humans now live on their world. 

Then there is another race the Kmet call the Dividers. Are they the reason the Kmet are afraid? Are they responsible for the destruction of a thriving human colony or did the Kmet do that themselves for some reason? Are they responsible for what might be called a divided world? Will the colonists give up the home they've built over the past century to return to New Earth? There are so many possibilities and so many potential misunderstandings.

This isn't a typical book for me because I generally prefer books that are about the characters while this is a book about the world building with minimal character story. As always Czerneda excels at introducing aliens that are truly alien and that's what makes this book worth reading. It's a good choice for anyone who hates Star Trek because the aliens are mostly humanoid and there isn't enough real science buried in the fiction. The concepts in To Each This World are all theoretically possible which is its own kind of magic.