The Language of Power by Rosemary Kirstein

Following a slim clue, the steerswoman Rowan comes to the city of Donner hoping to learn more about the master-wizard Slado. But as the new facts add up, a strange tale from the past emerges, a tale behind all the secrets of the present. Luckily, the Outskirter Bel is on hand to watch Rowan's back. Because there's one sure way to know that Rowan is on the right track: Someone will try to kill her.

The steerswoman Rowan has learned much about the master-wizard Slado: how his spells are devastating the distant lands known as the Outskirts, and how they will ultimately threaten even the Inner Lands. But she knows nothing else about him, not even why he is hiding his actions from the other wizards. He must be found, and stopped. Now, following the slimmest of clues, Rowan arrives in the city of Donner hoping to learn more about Slado's plans. But when the answers begin coming in faster than the questions can be asked, a strange tale from the past emerges, a tale behind all the secrets of the present... Fortunate that Rowan has the Outskirter warrior Bel on hand to watch her back. Because there's one sure way to know that the steerswoman is on the right track: Someone will try to kill her.