"The Mortal Engines Quartet" is a series of four young adult novels written by Philip Reeve. Set in a post-apocalyptic world where cities move on wheels and consume each other for resources, the story follows characters like Tom Natsworthy and Hester Shaw as they navigate a dangerous landscape filled with political intrigue and moral dilemmas. The series includes "Mortal Engines," "Predator's Gold," "Infernal Devices," and "A Darkling Plain." Each book explores themes of survival, technology, and the consequences of human actions, while introducing readers to a richly imagined universe filled with unique characters and inventive machinery.