" The Missing are a fifth tribe,” Theus said. “Part of the first wave to leave humanity’s home world an age before those who came here from the four systems. I was part of the final ascension that emptied Abeth long before the new tribes arrived, but some of my parents’ sect escaped the purification and managed to hide in the northern ice. It’s not a place to thrive. Their descendants remained a handful, leading primitive lives. I don’t know when or how they met the newcomers but they were not recognized and in time their bloods mingled, though their line stayed in the north. "
― Mark Lawrence , The Girl and the Mountain (Book of the Ice #2)