Vin assassinated the Lord Ruler in order to bring the Last Empire to an end and restore freedom. But the Deepness—the deadliest form of the ubiquitous mists—has returned, coupled with increasingly heavy ashfalls and increasingly severe earthquakes. The future of humanity appears to be bleak.
Emperor Elend Venture aspires to unearth clues left behind by the Lord Ruler that would allow him to redeem the world after escaping death at the climax of The Well of Ascension by becoming a Mistborn himself. Vin is tormented by remorse for being duped into releasing the mysterious force known as Ruin from the Well. Ruin wishes to annihilate the world, and its near omniscience and power to bend reality make it appear impossible to stop. Vin can't even discuss it with Elend for fear of Ruin discovering their plans!