The Duke's Ballad by Andre Norton
Witch World is the most popular and enduring series written by Science Fiction Grand Master Andre Norton. Since the 1960s, the novels of Witch World have enthralled millions of readers worldwide. Norton collaborated with Lyn McConchie to write the first new Witch World novel in more than a decade, a magical story of courage. The Duke's Ballad is the tale of Aisling, a young witch from a family gifted with magical power. But her brother, Kirion, wields a power he can gain only by a single, terrible means: by killing someone else who holds power. Years ago, Aisling fled Kars when Kirion, working for the Duke of Kars, tried to kill her. Now she has returned, in disguise, with her younger brother Keelan, to undermine Kirion's power and defeat the evil duke. Through guile, persistence and ingenuity, Aisling and Keelan must somehow find a way to avoid the attention of their dangerous older brother and save the people from his murderous sorcery.