The Darkling by David Kesterton (1982)
The Darkling, Kesterton's only novel, was one of the few books published by the legendary Arkham House from a slushpile. In the far future the world seems to be slowly dying. In the distant past there were two seasons. Now there are six: Spring, Bloom, Advent, Terror, Eve, and Umbra; during the last three, humanity hides in caves to avoid the darklings -- giant flying creatures who feast on humans. Mankind has devolved to a few small tribes, scattered in the north. One northman, Maradek, who has almost reached his maturity, has a vision about his missing father, Afurad. Afurad left the tribe six months ago to get a new bride from a neighboring tribe, never returned and is presumed dead. Maradek's vision told him that his father was alive and had got his bride who was now pregnant with the Great One, a savior who would rescue the world from the Terror and the deadly beasts who appear during that season.
Maradek sets out on a quest to find his father to bring him and the Great One home. Spring has not yet arrived and monsters roam the land as he begins his journey. He travels through a strange and terrible world, finding himself allied with an old plainsman, Zher-Geer, and his "servant," Kinit -- a telepathic Unique, the only of its kind.
The Darkling is a strange book, at first reading like William Hope Hodgson, then like Edgar
Rice Burroughs, and finally like a mash-up of Jack Vance, A. E. van Vogt, and Planet Stories. The book is quite an accomplishment for a first novel. I really liked it and, if you go for this sort of thing, I think you will, too.