"Mortal Engines" is a science fiction novel by Philip Reeve, set in a post-apocalyptic world where cities are mobile and consume smaller towns for resources. This concept, known as "Municipal Darwinism," leads to a society where survival depends on the ability to move and consume. The story follows Hester Shaw, a young woman seeking revenge against Thaddeus Valentine, a powerful figure in the city of London. As they navigate a dangerous landscape filled with rival cities and ancient technology, themes of power, survival, and morality emerge, highlighting the consequences of a world driven by greed and competition.