A realistic Snape's daughter story. Severus Snape discovers he has a daughter, born of a brief affair with Bellatrix Lestrange. First, a journey to reach the frightened, emotionally damaged child, and then a full-blown mental war, as Bellatrix manages to possess the girl from her cell in Azkaban. Among other things, an in-depth exploration of Occlumency. AU, in-character Snape.