Great story - don't mess with warlocks! They get their revenge.
Though the language can be flowery sometimes, this book is a nice branch off the King Arthur story. It takes place during the reign of King Henry II and Thomas Becket. Be aware that this is a romance as much as a fantasy.
Good enough to read out loud to my mother.
This series of Ace Fantasy Specials included War for the Oaks by Emma Bull(#1) (which is my VERY favorite fantasy book); Lord of the Crooked Paths by Patrick Adkins (#2) and this book.
" A king named Henry, his Chancellor Thomas at his side, ruled over Norman baron and Saxon peasant alike, in a country torn by strife. Then the knight who called himself Pendragon appeared, a skilled warrior with snow-white skin and sightless eyes like scarlet hell. He claimed descent from Arthur, king of legend, and rode with the fair Rosamund: herself of the blood of Merlin, greastest of all mages."