Felix Castor is a fictional character created by author Mike Carey. He is a freelance exorcist living in a contemporary London where supernatural beings, such as ghosts and demons, coexist with humans. Castor often finds himself navigating the complexities of this world while dealing with his own personal struggles and moral dilemmas. The series featuring Felix Castor includes several novels, starting with The Devil You Know. These books blend elements of urban fantasy, horror, and mystery, showcasing Castor's adventures as he confronts various supernatural threats while trying to maintain his humanity in a chaotic environment.