Plague from Within

From publisher blurb:

In Plague from Within, a group of level-4 adventurers meets the Kokin, a village of tiny fairy-people, like sprites. The Great Father Tree, their creator and protector, is plagued and diseased. The Kokins are dying and need help to cleanse their tree. When the heroes arrive, a group of mercenaries has already settled in. They tried to do the job but after measuring their losses on their first attempts decided it would be better to backstab the tiny people who hired them in the first place.

The Kokins depend on the heroes to survive, and even with their help, it doesn't guarantee a happy ending for them. Regardless of the adventurers' actions, the fate of the Kokins might already be written in stone and come to an end.