Tom is a 15-year-old Third Class Apprentice who works in the London Museum of History. Small and shy, he lacks a family or significant social circle, pouring his enthusiasm into a deep love for his traction city. He firmly believes in the propaganda of Municipal Darwinism until an unexpected fall into the Out-Country forces him to reconsider everything he knows about the bare earth.

Hester is a fierce, resourceful scavenger operating in the dangerous Hunting Grounds. A violent encounter in her childhood left her with a severe facial scar that resembles a furiously crossed-out portrait. She covers her face and lets a singular desire for revenge against the man who murdered her parents drive her every action.

Valentine is the charismatic head of the Guild of Historians, recognized by his silver-flecked black hair and trim beard. He presents himself as an adventurous, gentlemanly hero to the citizens of London, but he secretly harbors a ruthless instinct for self-preservation. He uses his past as an Out-Country scavenger to secure dangerous technology for the city's leadership.

Katherine is Thaddeus Valentine's privileged daughter, living a sheltered and comfortable existence on London's highest tier. She shares her father's gray eyes and dazzling smile, spending her days completely detached from the brutal labor that keeps the city moving. A sudden, violent incident involving her father prompts her to investigate the squalid lower levels of the city.

Crome is the Lord Mayor of London and the ruthless head of the Guild of Engineers. Described as thin and gloomy as an old crow, he is obsessed with securing resources and expanding the city's power at any cost. He directs the reconstruction of ancient, devastating technology, viewing any resulting destruction as a necessary step for municipal progress.

Anna Fang is a lean, capable aviator with badgery slashes of white in her black hair. A former slave, she built her own heavily armed airship, the Jenny Haniver, to secure her independence. She operates as a skilled agent for the Anti-Traction League, firmly believing that predator cities are an unsustainable blight on the planet.

Grike is a terrifying Stalker, a mechanical warrior created by fusing technology with a human corpse during the Sixty Minute War. He possesses a horrible voice that sounds like squealing cogs and a body designed for lethal efficiency. Despite his programming, he retains complex, protective emotions from his time raising a young outcast.

Bevis is an apprentice in the Guild of Engineers who is stationed in the turd tanks, London's dismal waste-management level. He observes a crucial altercation in the Gut but fears the consequences of speaking out. His knowledge of the city's underbelly makes him an essential guide for those investigating the mayor's secrets.

Pomeroy is the Deputy Director of the Guild of Historians and the direct supervisor of the museum's apprentices. He represents the traditional, cautious attitude of the Historians, prioritizing the quiet preservation of artifacts over the aggressive, forward-looking violence of the Engineers.

Pandora Shaw is Hester's murdered mother and a former researcher. Though she exists only in the memories of those she left behind, her past work tracking down ancient weaponry from the Sixty Minute War sets the entire conflict of the narrative in motion.

Dr. Arkengarth is an elderly historian working at the London Museum. His casual knowledge of past expeditions and the origins of specific artifacts provides critical context that helps untangle the mystery surrounding a highly coveted piece of ancient technology.