"The City of Mirrors" is the third book in the Passage Trilogy by Justin Cronin. It continues the story of a post-apocalyptic world where humanity struggles against vampire-like creatures known as virals. The narrative explores themes of survival, sacrifice, and the enduring nature of hope. The novel follows several characters, including Amy Harper Bellafonte and Peter, as they navigate the challenges of their transformed world. The story delves into the origins of the virals and the impact of their existence on human society, ultimately leading to a climactic confrontation between the two groups.