Even as humans can be, the Kel'Regar, too, can be touched by madness, and it can drive them to push to ends incomprehensible by the sane. The work of one such, Kararemi'ar'Salm'Torat, the Menangerie of Mad Creation, is a twisted, living structure, tormented by years of loneliness and incomprehensible need.
The secret for immortality has been discovered by an eccentric wizard/mad scientist. Its found you need to reapply once a month. As people stop dying, and the birth rate increases exponentially, people are forced into homelessness, because of the need for food reamins the same, and food is not being produced fast enough to feed the undying population. The PCs have to find the creator and kill him, and destroy production, to save the world from undying, unending torture from hungryness.