The Lost Steersman by Rosemary Kirstein

The steerswoman Rowan knows that the fall of the Guidestar and the massacre of Outskirter tribes were caused by one man: the secret master-wizard, Slado. Now, to find him, she comes to Alemeth, where centuries of records might provide clues in her search. But when death from the wildlands invades sleepy Alemeth, Rowan has new, urgent questions, and cannot wait for answers to act...

How do you find someone? How, if you have never seen him, never heard him described, did not know where he lived? How, if he wished not to be found? And how, most especially, if he were the most powerful wizard in the world? The steerswoman Rowan has discovered that the fall of the Guidestar and the massacre of Outskirter tribes were caused by one man: the secret master-wizard, Slado. But until now, no steerswoman had known of his existence, nor knew that the wizards answered to any single authority. Now, Rowan must find him. She comes to the seaside town of Alemeth, where centuries of records might help her find clues for her search. Then, an unexpected encounter with a lost friend: Janus, a steersman who had resigned his membership in the Steerswomen, giving no explanation. Now Rowan has hope for help in her search -- but Janus has changed. The bright intellect is now shrouded in a dark, shattered spirit...Then death comes to sleepy Alemeth, monsters from the Outskirts, and Rowan can not help but wonder: are all these strange events connected?