Flux

The final book in the entire series shows Zell and his friends on a quest to prove Human intelligence and worthiness as a species.
 

They go on a trek to discover the elusive Human Elders, hoping to find old technology and an ally for their vision to free all Humans on the planet and create a world where both species cooperate and thrive with mutual respect.
 

Once again, Zell and his friends face natural hazards, have difficult encounters and must deal with hate on an even larger scale.

Best reading order for the Franssisi Four Chronicles:
Decoy (Prequel)CaptiveFugitiveCatalystFulcrumFlux