What happens in mortal engines by Phillip Reeves?

In "Mortal Engines" by Philip Reeve, a post-apocalyptic world is depicted where cities move on giant wheels, scavenging resources from smaller towns. The story follows Hester Shaw, a young woman seeking revenge for her mother's death, and Tom Natsworthy, an apprentice in London. Their fates intertwine as they uncover a conspiracy involving an ancient weapon capable of destroying cities. Together, they navigate a dangerous landscape, challenging the power dynamics between mobile cities and the remnants of civilization.