Exorcist Lucian Negru was forced to make a terrible choice sixteen years ago: in helping his twin sister, Catarina, he left his lover, Rachael, to Hell. Unfortunately, Catarina made a deal with the Fallen Angels and wanted Lucian's support in gathering followers in a war to storm Heaven itself. When Lucian refused, Catarina had him crippled and made to live like a prisoner.

When Lucian hears that Rachael's soul has almost been devoured by the demon possessing her, he flees Catarina's fortress. While on the run, Lucian sees a young girl crossing over from Earth to Hell and knows that he must protect her or she will not survive. First Lucian has to break his word never to open a Hell Gate so that he can rescue the girl from Hell. Then he has to teach her about Woerld and her own powers so that she can survive.

Twelve-year-old Lindsay Richardson is on her way back from a ballet lesson when the Crimsom Veil opens and deposits her on a hostile, alien world. Confused and disoriented, her only ally is a crippled old man, and she cannot know if she should trust him. Lucian starts to tell her about this new Woerld and the war between Heaven and Hell which is fought upon it, but it sounds like Sunday School tales to her.

The Woerld is a parallel dimension between Earth, Hell, and Heaven. Its warriors try to protect Earth and Heaven from the Fallen. The most powerful soldiers, called the Katharoi, can call upon the power of God (here meaning any religion's primary deity) to cast spells and use their own special powers. There is explicit mention of Christian, Jewish, and Islamic God, Wiccan Goddess, and a reference to a Hindu city. The different religions work together against the Fallen, who have already conquered the Zoroastrian fortress and are constantly looking to convert people from the other cities.

Judge Rachael Boucher has been fighting against the demon Wyrm inside her for sixteen years. She remains the Heir to the Citadel, but many people think her to be corrupted beyond redemption. Exorcists have tried to call out the demon but failed. Now she has been charged with finding Lucian and bringing him to be judged for his crimes. She knows that he has opened a Hell Gate and thereby broken his word.

Rachael and Lucian intense shared history has left them both deeply scarred. Most people are convinced that Lucian is working with his sister for the Fallen. Rachael doesn't know if she can trust him at all. Lucian is trying to protect Lindsay but also trying to keep emotional distance from her so that she will not be tainted by association. He knows that if they survive, the authorities at the Citadel will separate them, for her sake.

Unfortunately, the villains of the book remain more one-dimensional. Catarina is dependent on Lucian and sacrifices her feelings to her demonic familiar, but her primary motivation seems to be simple hunger for power. The motivations of the other villains remain mostly a mystery. The first few chapters also occasionally feel confusing.

Miserere is an intense, darkly atmospheric novel with flawed characters set in a dark, desperate place.