Web Of Light: Marion Zimmer Bradley

Book I of The Fall Of Atlantis. Domaris, disciple of the Temple of Light, was wrenched from her peaceful life by the arrival of the Atlantean prince Micon, whose powers over wind and sun, earth and fire are coveted by the sorcerers of the dark who would harness his gifts for their own evil ends. Soon, out of a tender, earthly passion, would rise forces that might decide the final victory. Soon, Domaris would bear Micon a son - but Deoris, her sister, would be enthralled by the forces of darkness.