Sorcerer's Son — Phyllis Eisenstein

Gildrum came to Castle Spinweb as a wounded knight, to be succored by the Lady Delivev, a sorcerer with control over all magic related to spinning or weaving. Then, after a brief idyll of love, he vanished, leaving behind

A WOMAN WAILING FOR A DEMON LOVER

But neither she nor Cray, the son she bore, could know that Gildrum was a demon, enslaved by the evil sorcerer Rezhyk. Nor could Gildrum return to the woman he had come to love. He could only watch helplessly as Cray set out to find the knight who never was, guarded from peril by the webs of ensorcelled spiders.

Frustrated at every step, Cray turned at last to grimmer sorcery for his answers. And thus he came under the control of his mother's arch- enemy--the demon-master Rezhyk.