The Hero of Ages (Mistborn Book 3) by Brandon Sanderson - mass market

Now with over 10 million copies sold, The Mistborn Series has the thrills of a heist story, the twistiness of political intrigue, and the epic scale of a landmark fantasy saga.

Vin fulfilled the prophecy and released the power gathered in the Well of Ascension. But it was all a trick, and now the godlike being Ruin has been unleashed on the world, bent on its destruction by earthquake and Fire.

Having escaped death only through becoming a Mistborn himself, Emperor Elend Venture now hopes to find clues left behind by the Lord Ruler that will help them fight back. Legends speak of a hero, but were any prophecies not corrupted? To make up for being duped, Vin must unravel the truth so she can become the Hero of Ages before Ruin can wipe out all life on the planet.