Meghan is a 40-year-old nurse living in an apartment under the Chicago transit tracks with her teenage daughter. She works hard to project the image of a compassionate caretaker, often placing the physical and emotional needs of others before her own. Underneath her capable exterior, she carries unresolved grief over her sister's death and extreme anxiety regarding her daughter's safety in the city.

Caitlin is a 32-year-old woman resting in a coma after sustaining severe head injuries from a fall. She recently moved back to Chicago from California, though her parents were unaware of her return. Her history and personality largely unfold through the tense discussions and differing accounts provided by her visitors.

Ben is Meghan's ex-husband and shares custody of their daughter. He lives in a condo and maintains a steady presence in Sienna's life, though he and Meghan often argue over parenting decisions and finances. He attempts to move on from his marriage by dating, which causes friction in his co-parenting dynamic.

Sienna is Meghan and Ben's 16-year-old daughter. She splits her time between her mother's apartment and her father's condo. She exhibits a stubborn streak and frequently pushes boundaries, challenging her mother's rules while dealing with the lingering fallout of her parents' divorce.

Luke is an older nurse who works closely with Meghan in the ICU. He serves as a reliable friend and sounding board for her personal problems. Outside of the hospital, he experiences significant financial pressure and tension at home with his pregnant wife.

Tom is Caitlin's father and an employee at a law firm. He spends hours at the hospital trying to logically process his daughter's trauma through research. He harbors quiet frustrations regarding his family's difficult history with Caitlin and tries to protect his wife from further distress.

Amelia is Caitlin's distressed mother. She leans heavily on the nursing staff, particularly Meghan, for emotional support during her vigil at the hospital. She appears worn down by years of familial tension and past conflicts regarding her children.

Jackson is Caitlin's brother who supposedly travels from London after hearing about her fall. He exhibits an unemotional, detached demeanor regarding his sister's critical condition, raising questions about his true feelings.

Penelope is Luke's pregnant wife. She is currently on bedrest and experiences deep frustration over her husband's long hours and their mounting financial struggles.

Milo is a strange man who frequently lingers around the hospital to observe Caitlin. His evasive behavior and unauthorized presence in the ICU create immediate tension for the nursing staff.

Nico is a teenage boy who is friends with Sienna. He visits her at the apartment, contributing to Meghan's anxiety regarding her daughter's growing independence.

Bethany is Meghan's younger sister who died by suicide the year after Meghan graduated from high school. Her passing remains a source of deep, unresolved sorrow that influences how Meghan views her patients.

Evan is the new downstairs neighbor in Meghan's building. He introduces himself to Sienna, which immediately triggers Meghan's protective instincts and fear of strangers.

Natalia is a nurse in the ICU who works alongside Meghan. She discusses patient cases and assists with the daily operations of the hospital floor.

Bridget is a nurse who briefs Meghan on incoming patients. She provides the initial medical context regarding the severe injuries on the ward.