Mary is a teenage girl living in a heavily fortified village surrounded by the undead. She chafes against the restrictive rules of the Sisterhood and dreams of finding the ocean, a place of freedom her mother describes in forbidden stories. Fiercely independent, she seeks to reconcile her personal desires with the strict social expectations placed upon young women in her community.

Jed is Mary's older brother and a Guardian of the village, tasked with protecting the borders from the Unconsecrated. He is deeply devoted to his wife, Beth, and carries a heavy burden of grief following a series of family tragedies. His strict adherence to village rules and his sense of duty often put him at odds with Mary's rebellious nature.

Travis is the younger brother of Harry and Beth, and the object of Mary's secret affections. He shares some of Mary's curiosity about the outside world but is more inclined to accept a peaceful, traditional life within the village boundaries. His gentle nature and romantic connection with Mary complicate the community's arranged marriage customs.

Harry is an Apprentice Guardian and the practical, protective brother of Travis and Beth. He adheres to the village's traditional customs and formally steps forward to speak for Mary, claiming her as his betrothed. He serves as a steady, reliable presence, though he struggles to understand Mary's yearning for the world beyond the fences.

Sister Tabitha is the formidable head of the Sisterhood, the religious authority that governs the village. She strictly enforces the community's rigid laws, demanding absolute obedience and prioritizing tradition over individual happiness. She views curiosity about the outside world as a dangerous threat to the village's survival and works to suppress it.

Cass is Mary's closest childhood friend and one of the only other girls their age in the village. She is highly respectful of the village's moral codes and social pressures, accepting her arranged betrothal to Travis despite harboring secret feelings for his brother. She favors stability and tradition over rebellion.

Gabrielle is a teenage girl whose sudden arrival in the village proves that other human settlements exist. Dressed in unusual, brightly colored clothing, she represents the mysteries of the outside world that Mary desperately wishes to uncover. Her presence in the Cathedral becomes a catalyst for Mary's investigation into the Sisterhood's secrets.

Beth is Jed's wife and the sister of Harry and Travis. She experiences early hardships with a difficult pregnancy, tying her to the Cathedral's hospital for bed rest. She represents the fragile nature of family and motherhood within the dangerous confines of the village.

Mary's mother is a grieving widow who obsessively watches the fences for her lost husband. She instills a sense of wonder in Mary by sharing forbidden stories about the fabled ocean, passing down a legacy of hope that contrasts sharply with the village's grim reality.

Jacob is a young, vulnerable boy from the village who requires protection during times of chaos. He becomes a symbol of innocence and represents the heavy responsibility the older characters carry as they attempt to survive.

Argos is a loyal puppy gifted to Mary. He serves as a source of comfort, companionship, and early-warning protection against the undead, bringing moments of lightness to the grim survival conditions.