A 22-year-old college student attending UC Davis in 1996. Raised in an unusual family dynamic where her father continuously studied her behavior, she struggles with socialization and often feels out of place among her peers. She tries to maintain a low profile and harbors deep anxieties about her missing siblings, using silence as a defense mechanism to avoid processing her grief.

Rosemary's twin sister who was sent away when they were five years old. She and Rosemary were inseparable during their early childhood, sharing a deeply interconnected bond and participating together in their father's behavioral studies. Her sudden disappearance permanently fractured the family and left her siblings with profound psychological scars.

Rosemary's father and a committed, highly analytical psychologist. His career and rigorous behavioral studies dictate the family's unusual lifestyle. He prefers to view human behavior through a strictly scientific lens, which often leaves his children feeling as though they must earn his affection through performance.

A deeply loving but emotionally fragile woman who serves as the peacemaker in the Cooke household. While her husband conducts the scientific aspects of raising their children, she handles the day-to-day mothering and physical care. The sudden loss of her children pushes her into severe depressive episodes, leaving her withdrawn.

Rosemary's fiercely stubborn older brother. As a child, he openly questions his father's scientific methods and exhibits deep loyalty to his sister Fern. His inability to accept Fern's sudden removal from their home drives a wedge between him and his parents, leading him to run away and live off the grid as a radical activist.

A charismatic and chaotic drama major who abruptly enters Rosemary's life. She enjoys pushing social boundaries, breaking rules, and manipulating situations to her advantage. Her uninhibited nature contrasts sharply with Rosemary's repressed personality, making her an exciting but unpredictable influence.

Harlow's on-again, off-again boyfriend. He projects a confident, somewhat arrogant demeanor but frequently finds himself at the mercy of Harlow's chaotic whims. He is often loud and dismissive of others, particularly when discussing literature or social issues.

The elusive and conspiracy-minded manager of Rosemary's apartment complex. He fancies himself a protector and becomes quickly infatuated with Harlow. He harbors strange beliefs about his tenants and desires to be part of something more exciting than his day job.

Rosemary's college roommate. He is generally supportive but easily frustrated by the chaotic elements Rosemary brings into their shared living space, particularly when strangers occupy their home.

Rosemary's maternal grandmother. She strongly disapproves of Vince's profession and his unusual child-rearing experiments. She frequently steps in to help care for Rosemary when her daughter experiences depressive episodes.

Lowell's high school girlfriend. She had a tumultuous relationship with him before his sudden disappearance and holds residual frustration regarding his abrupt departure from her life.

A college professor who teaches a course on religion and violence. His lectures on social behavior and gender dynamics deeply unsettle Rosemary, who finds his interpretations heavily skewed by his own biases.

One of Vince's graduate students who assists with the family's home-based research. He acts as an observer during the children's early years and is tasked with ensuring Fern's physical safety during her relocation.

A campus police officer who takes a strict approach to student disturbances. He arrests the girls after a cafeteria brawl but drops the charges against Rosemary after speaking with her father.