Finn is an 18-year-old inmate in the high-tech, sentient prison known as Incarceron. He lacks memories of his life prior to three years ago and experiences visions that others attribute to his being "cell-born." Bearing a mysterious eagle tattoo on his wrist, he is driven by an intense desire to escape and discover his true origins.

Claudia is the nearly 18-year-old daughter of Incarceron's Warden, living a privileged but highly restricted life outside the prison. She despises the kingdom's "Era" laws that forbid modern technology and bristles against her father's controlling expectations. Intelligent and rebellious, she uses illegal devices and subterfuge to investigate the kingdom's secrets and avoid her arranged marriage.

Keiro is an inmate of Incarceron and Finn's oathbrother within the Comitatus gang. He is charming, pragmatic, and ruthless, willing to use violence and trickery to survive the prison's harsh environment. Despite his self-serving attitude and frequent conflicts with others, he maintains a strong bond of loyalty to Finn.

John Arlex serves as the Warden of Incarceron, the only person supposedly aware of the prison's true nature and location. He presents a stern, calculating demeanor and enforces the kingdom's strict, anti-technology laws while hiding complex secrets in his private study. He prioritizes political maneuvering, arranging his daughter's marriage to secure power within the kingdom.

Jared is a Sapient who serves as Claudia's private, live-in tutor. He is intellectual, kind, and deeply curious, secretly maintaining a collection of illegal technological devices to aid in his research. He acts as Claudia's closest confidant and helps her investigate the mysteries surrounding the kingdom and Incarceron.

Queen Sia is the mysterious and power-hungry ruler of the kingdom. Her origins are entirely unknown, adding to rumors that she is a sorceress. She aggressively maneuvers to secure her biological son's place on the throne, utilizing blackmail, espionage, and ruthless politics to eliminate anyone who stands in her way.

Incarceron is a massive, high-tech, sentient prison designed by the Sapienti to be a utopia. Over time, it has developed its own consciousness and transformed into a harsh, punitive environment. It constantly monitors its inmates through millions of red eyes, actively working to prevent anyone from leaving its confines.

Caspar is Queen Sia's biological son and the heir to the throne. He is irresponsible, shallow, and entirely uninterested in his future duties as king or his impending marriage to Claudia. He frequently engages in scandalous behavior and openly admits to planning a life of infidelity after the wedding.

Gildas is an older inmate of Incarceron and a member of the Sapienti, a group of learned men. He possesses extensive but outdated knowledge and clings fervently to the legends of Sapphique, the only person said to have escaped the prison. He joins Finn's group, hoping that Finn's visions will guide them to freedom.

Attia is a young woman imprisoned in Incarceron who survives by concealing her gender and health beneath layers of rags and fake sores. Initially enslaved by the Comitatus gang, she is freed with Finn's help and becomes a fiercely loyal, resourceful member of his escape group.

Giles is the deceased son of the former king and Claudia's original betrothed. Before his sudden and highly suspicious death from a horseback riding accident at age 15, he was known to be a happy child who became withdrawn after his father passed away.

Jormanric is the ruthless "Winglord" of the Comitatus gang inside Incarceron. He maintains control through violence and intimidation, wearing seven skull rings that he believes grant him extra lives. He surrounds himself with bodyguards and forces enslaved people to test his food for poison.

Lord Evian serves as Queen Sia's Chancellor but secretly leads a conspiracy group known as the Steel Wolves. He is desperate to overthrow the restrictive "Era" laws and the current administration, actively seeking Claudia's assistance in his dangerous plots against the royal family.

Maestra is a member of the Civicry gang within Incarceron. During a raid, she recognizes the eagle tattoo on Finn's wrist, leading him to take her hostage in hopes of uncovering information about his past.

Bartlett is a loyal servant who raised Giles from a young age. Following Giles's suspicious death, Bartlett wrote a secret testimony outlining the inconsistencies surrounding the tragedy before being murdered to protect the kingdom's secrets.

Medlicote is the Warden's trusted secretary. Despite his position, he is strictly forbidden from entering the Warden's secret study, reflecting the extreme secrecy maintained by his employer.

Alys is Claudia's nurse and one of the primary caregivers who raised her in the Warden's frequent absences. She enforces the household's routines and protocols.

Fax is Caspar's personal bodyguard. He is observant and reports suspicious activities back to his superiors, ensuring the prince's safety and surveillance.

Job is a child servant working on the Warden's estate. He provides Claudia with basic information regarding the local residents.

Helena is the deceased wife of the Warden. According to the Warden, theirs was a loving marriage that tragically ended when she died in childbirth, a fate exacerbated by the kingdom's ban on modern medicine.