To Save a World (Darkover Omnibus #7)

An omnibus volume of two of Marion Zimmer Bradley's classic, long-unavailable Darkover novels, including the first Darkover novel ever written!
To Save a World includes The World Wreckers and the Planet Savers, plus the short story "The Waterfall."
The Planet Savers:

Originally published in Amazing Stories in December 1958, The Planet Savers was the very firs Darkover novel to see print. It was here readers were first introduced to the now legendary world of Cottman IV, at a time when the Terrans are desperately seeking a cure to a disease of epidemic proportions that threatens the lives of Terrans and Darkovans alike.
 
For every forty-eight years, Trailmen’s fever, a childhood illness among this native and venerable race, becomes pandemic, decimating the human population of this rustic planet. Now, one brave Terran doctor must join a Darkovan expedition into the wild mountainous...