Freedom's Challenge by Anne McCaffrey - USED

SCIENCE FICTION. The inhabitants of Botany - a mixture of humans and extra terrestrials - had managed to build a thriving and productive world out of what had originally been intended as a slave planet. And now they had plans to try and overthrow the terrible Eosi, who for centuries had existed by subsuming members of the Catteni race, living in their bodies and ruling space through them. And the Botanists had received mysterious and unexpected help from the great beings they knew only as 'Farmers' - for the Farmers had thrown a huge impervious space bubble round Botany. Even as the Eosi ships tried to pulverise the rebellious planet, the bubble held firm. But, safe though they were behind the protective device, Kris Bjornsen, Zainal and all of the Council knew they had to go out and destroy the Eosi on their own ground. It fell to Zainal to risk his life in a desperate and daring mission to vanquish the monster life forms forever.