Two legendary Andre Norton SF adventure novels in one omni volume.
Here Abide Monsters: On a world where parallel and alternate universes intersect Celtic faery folk, modern humans, and inhabitants of a distant future share the planet's surface. There are also aliens in flying saucers which are capturing and enslaving new arrivals who fall through the "gates." One group of new arrivals meets a protector, a man who calls himself the Herald. He promises safety—but in exchange, he requires a piece of their souls in payment.
Yurth Burden: Two races share Zacar: the plains dwelling Raski and the mountain dwelling telepaths, the Yurth. The two are often in contention along their borders, and terrible war periodically breaks out between them. When a young Yurth woman goes on her coming of age vision quest, one young Raski warrior follows her—and together they discover a secret that will surely unbalance their world and may change Zacar forever.