The Gift (Pellinor, #1) - Alison Croggon
This is the first in a series of four books, published under different titles (The Gift or The Naming) depending on where you are in the world...

Our protagonist is Maerad, a slave in a grim holding on the edge of the mountains, who manages to keep a low profile and avoid the worst of treatment by pretending she is a witch. She knows nothing of her background, her only memories being of that place and her mother, now dead.

Naturally, otherwise The Naming would be a very short and somewhat dull book, Maerad is more than she seems, as she is about to discover. First she must leave the only place she has ever known, in the company of Cadvan, a man who only she can see - he tells her that is because she can do magic, like him, otherwise he would be invisible to her as well.

Despite her fears, Maerad accompanies Cadvan on his travels - he's been tasked with discovering what is going on, as the bards who were meant to provide for the people and keep the land safe have been falling down on the job. As the two of them travel, Maerad discovers more about herself and also about Cadvan, as well as discovering the part she is apparently supposed to play in turning back the tide of darkness that threatens to overtake everything.

It's clear that the author has put a lot of thought into the worldbuilding in this series, though a meaner editor could have helped immensely with trimming the unnecessary description she seems equally determined to put in everywhere. At times, that over-use of adjectives distracts from the storyline, and that's never a good sign. The next book in the series is The Riddle.