Casey is a 29-year-old medical resident working in a Chicago hospital when a mysterious virus causes society to collapse. Growing up, she harbored deep resentment toward her father's rigid survivalist training and the social isolation it caused her. Now immune to the virus due to an early bite, she relies on her medical knowledge and long-dormant combat skills to survive. She wields throwing stars and a combat knife to defend herself in a violent new reality.

Blake is a former Navy SEAL who tormented Casey during their high school years. He currently lives at Dale's compound, functioning as a highly capable guard and Dale's trusted right-hand man. His physical transformation and intense combat skills clash with Casey's traumatic memories of him as a cruel teenager.

Dale is Casey's physically imposing father, whose life is entirely defined by his obsession with doomsday prepping. Driven by the tragic murder of his wife, he has spent years transforming his rural Wisconsin property into a fortified compound. His strict methods alienated his daughter, though his extreme preparations prove lifesaving when society falls.

Nate is a handsome doctor engaged to Casey before the outbreak. He embodies the civilized, professional world Casey sought out to escape her survivalist upbringing. Accustomed to modern conveniences and structure, he struggles to adapt when the virus unleashes feral attackers into their hospital.

The burners are a loose collective of uninfected human survivors who exploit the societal collapse for personal gain. They roam the cities and rural areas as violent predators. They utilize deception, organized tactics, and sheer brutality to steal resources and terrorize others.

Tessa is Casey's loyal childhood friend who takes refuge at the Wisconsin compound. She maintains a cynical wit and pragmatic outlook on the apocalypse. She offers a sense of stability and emotional grounding for Casey amidst the chaos of the ruined world.

Greg is JJ's younger brother and Casey's cousin. He lacks the disciplined combat skills of the other compound guards, frequently making tactical blunders. He brings a lighter energy to the grim survivalist setting through his impulsive behavior and dramatic romantic life.

JJ is Casey's cousin who helps patrol and secure Dale's fortified property. He is diligent in his guard duties and deeply relieved by Casey's safe return. He operates as a reliable defender within the family's survival network.

Elaine is an older neighbor who provided shelter to a young Casey during a childhood tragedy. She functions as Dale's partner and a stabilizing presence for the extended family group. She quietly manages a dependency on insulin in a world with dwindling medical supplies.

Molly is a young woman taking refuge at the compound who is highly enthusiastic about her relationship with Greg. Initially intended to be a brief romantic encounter before the outbreak, she finds herself permanently attached to his family in the new world.

Chris is a survivor whose car broke down near the property, leading Dale to take his family in. He contributes to the compound's daily labor and defense.

Helen is a refugee at the compound who arrived with her husband and their two sons. She works to maintain a semblance of domestic routine in the apocalyptic environment.

Julie is Casey's aunt, living and working within the compound. She helps maintain the family's extensive weapons cache and participates in the group's coordinated defense strategies.

Jimmy is Casey's uncle who assists with compound maintenance and defense. He operates alongside the rest of the extended family to keep Dale's survivalist systems running smoothly.

Meredith is Tessa's mother, who evacuated to the Wisconsin property alongside her daughter when the virus began to spread.

Grant is a fellow Navy SEAL and close friend of Blake. He fell ill and lost his memory at the start of the outbreak, prompting Blake to bring him to a hospital.