Piper is a 13-year-old orphan surviving in the toxic environment of Scrap Town Number Sixteen. She earns her keep by scavenging meteor fields and fixing broken mechanical artifacts with a remarkable, intuitive skill. Desperate to avoid working in the southern iron factories that killed her father, she seizes a chance for a better life when she rescues a mysterious, tattooed girl from a caravan wreck.

Anna is an 11-year-old girl who awakens with complete amnesia following a catastrophic caravan crash. She bears a rare dragonfly tattoo that marks her as a protected subject of the southern king. Despite her physical fragility and lack of personal memories, she retains an encyclopedic knowledge of book facts and immediately bonds with her rescuer.

Gee is a scruffy 13-year-old boy serving as the chief of security for the 401 train. Sold into slavery by his parents at age seven, he harbors deep physical and emotional scars from his past. He relies entirely on his adopted train family and patrols the skies above the tracks, using his unique physical abilities to protect the locomotive from bandits.

Master Doloman serves as the master machinist for the King of the Dragonfly territories. He dresses wealthy and initially presents himself as Anna's concerned father, but he quickly resorts to violence and bribery to capture her. He commands immense resources and utilizes criminal slavers to track the girls across the continent.

Trimble works as the fireman and resident healer aboard the 401 locomotive. He constantly wears a belt full of glass vials containing various medicinal potions. Because he possesses an innate immunity to fire, he easily handles the train's massive engine and relates closely to others who possess unusual natural gifts.

Jeyne is a pragmatic, grey-haired engineer who commands the 401 train. She operates the massive locomotive using a fully functional metal arm. Constantly worried about her aging train being sent to the scrap heap, she acts as a strict but fiercely protective maternal figure to her eclectic crew of outcasts.

Raenoll belongs to the amphibious sarnun species and lives in the subterranean tunnels of Tevshal to avoid direct sunlight. She communicates telepathically and earns her living by reading the history of objects through touch. Her heightened intuition allows her to glimpse the hidden origins of people who seek her out.

Micah is a reckless nine-year-old boy living in the poverty of Scrap Town Number Sixteen. He scavenges the dangerous meteor fields for valuable debris, often ignoring safety protocols to beat older competitors to the best finds. He relies on Piper to repair his salvaged items so he can sell them.

Jory is Micah's older brother and fellow resident of the scrap town. He takes a highly practical and cautious approach to survival, contrasting sharply with his sibling's recklessness. He acts quickly to find medical help when disaster strikes during a toxic atmospheric storm.

King Aron rules the southern Dragonfly territories. He focuses entirely on expanding his domain through advanced steamships and exploratory aircraft. His massive demand for iron to build these machines drives the economy but also endangers the poorer workers who toil in his toxic factories.