Copper Skin, Oaken Lungs. Copper & Ash, #1

For a thousand years, The Old Town has stood as humanity's last bastion against the maalkonis, malignant black mists that reduced the rest of the world to ash. They are kept at bay by rusty machines on the town's walls. In order to survive, the dwindling population depends on one another. Since a young age, Justine has embraced the harsh responsibilities that accompanied her apprenticeship on the last farm in existence.
Her younger sister, Anna, is beginning her own apprenticeship as well. Learning engineering was not Anna's first choice, but the town's last mage fell to the maalkonis years prior, leaving nothing behind but confusing books and strange runes. When food runs low during a particularly harsh winter, distrust spreads like a plague, and Justine is blamed for it. As hunger leads to violence, she and her siblings are forced to flee The Old Town, embarking on a perilous journey into the very mists that had formed their cage.
Their fight to survive in the dark develops into a hopeful mystery as they follow the breadcrumbs of a mage's efforts to save the world. Meanwhile something pursues them through the maalkonis...