Fiona is a 17-year-old girl who awakens with amnesia after four years in a medically-induced coma. She bears a mysterious "Level Ten" spider-like tattoo on her hand, marking her as having received multiple doses of a bee flu vaccine. Once a talented classical pianist from a military family, she relies on her strong survival instincts to stay alive in a ruined world where she is hunted by beasts, raiders, and the militia.

Dreyden is a 17-year-old militia officer stationed at the south gate of the protective wall. He recognizes Fiona from their past as neighbors before the societal collapse. Though he projects a harsh exterior to his fellow militiamen, he harbors traumatic memories of losing his mother to raiders. He struggles to perform his tough duties while managing his protective instincts toward Fiona.

Jonah is Fiona's twin brother who has succumbed to the severe effects of the bee flu vaccine. He is marked as a "Level Ten" and exhibits extreme rage alongside superhuman strength. Before the collapse, he was a sweet boy who loved science fiction, but he now roams the dangerous world outside the wall acting aggressively toward anyone he encounters.

Governor Jacoby Soneschen is the local authority figure who rules the safe zone located inside the wall. He commands the militia and dictates the strict laws that govern the surviving population. He controls vital resources and places a massive bounty on Fiona's capture, demonstrating his power over the fragmented society.

Arrin/Arris is a young, starving survivor living in the dark, sewage-filled tunnels beneath the ruined city. Cunning and hardened by the dystopian environment, this survivor forces Fiona into a dangerous rescue scheme through threats and coercion. They possess intense survival skills and use the harsh underground network to hide from surface threats like the militia.

Lissa is Fiona and Jonah's older sister. According to Dreyden Bowen, she managed to secure a place living safely behind the wall, where educated and healthy individuals are permitted to reside away from the dangers of infected beasts and violent raiders.

Duncan is Dreyden Bowen's older brother. He successfully gained entry to live inside the wall, leaving Dreyden behind in the dangerous outer zones. He now serves in the militarized Inner Guard under the command of Governor Soneschen.

Jacqui is a former school acquaintance of Fiona's who survives in the ruined neighborhood. She provides Fiona with a few peanut butter crackers and frantically warns her to cut her hair and hide her gender to stay safe in the dangerous new world.

Ellen is the mother of Jacqui and a former neighbor of the Tarsis family. She survives in the dangerous neighborhood and spends her time attempting to manually pollinate green corn stalks with a paintbrush due to the extinction of honeybees.

Tommy is a member of the militia camp where Fiona is held captive. He is rough, highly suspicious of Fiona's "Level Ten" status, and frequently questions Dreyden Bowen's lenient treatment of their prisoner.

Len is a greedy and opportunistic member of the militia camp. Driven by a desire to gain enough wealth to buy his way inside the wall, he plots to kidnap and sell Fiona once he realizes her true value on the black market.

Micklemoore is an officer in the militia camp who uses a metal scanner to read the tattoos of captured individuals. He treats prisoners strictly by protocol and is visibly terrified when Fiona's scan triggers a flashing Level Ten alarm.

Dr. Grayson is a medical professional working within the government's lab system. He was deeply involved in the early medical responses to the bee flu and the violent side effects of the vaccine, placing patients like Fiona into comas while attempting to mitigate the crisis.