Lena is a 17-year-old girl living with her aunt's family in the enclosed city of Portland. Following the loss of her parents, she struggles with feelings of insecurity and fears the intense emotions she sometimes experiences. She initially looks forward to receiving the cure for the "disease" of love, believing it will bring her lasting peace and normalcy.

Alex is a 19-year-old who works as a security guard for the medical labs in Portland. He exhibits a calm, observant demeanor and bears the three needlepoint scars that mark him as a cured citizen. He is drawn to Lena and displays a quiet confidence that contrasts with the strict regulations of their society.

Hana is a 17-year-old girl and Lena's best friend since the second grade. Coming from a wealthy family, she possesses a fearless and outgoing personality that makes her highly visible among her peers. She openly questions the government's rules and listens to unapproved music. She frequently attends secret, illegal parties.

Carol is Lena's aunt and primary guardian. She is a fully cured citizen who enforces household rules and strongly believes in the necessity of the government's procedures. She maintains order in her home, which houses her husband, nieces, and granddaughters.

Rachel is Lena's older sister. Since receiving her cure, she exhibits a highly restrained and predictable personality, lacking the vibrant affection she showed during childhood. She is married with two children and fully conforms to the societal expectations placed upon adult citizens.

Grace is Lena's six-year-old cousin, the daughter of the late Marcia Tiddle. She is widely believed by the family to be completely mute. However, she actively observes everything happening in the household and shares a silent understanding with Lena.

Jenny is a nine-year-old girl residing with her grandparents, Carol and William. She is the older daughter of the late Marcia Tiddle and often displays a brash, disruptive attitude that annoys Lena.

William is Carol's husband and Lena's uncle. As a cured adult, he is a conforming, pro-government citizen who helps raise his grandchildren after the death of his daughter, Marcia. He manages a local convenience store where Lena works.

Marcia is the late daughter of Carol and William, and the mother of Grace and Jenny. Her life ended in a heart attack after her scientist husband disappeared under suspicion of being a sympathizer, leaving her young daughters to be raised by their grandparents.

Brian is a cured young man whom the government assigns as an approved marital match for Lena. He is practical and direct, having already undergone his own cure, which has stabilized his emotions and given him absolute faith in the procedure's benefits.

Lena's mother is a figure from the past whose profound grief over her husband's death from cancer led to three unsuccessful government curing procedures. Her history of intense emotional struggles deeply shapes Lena's initial fears about the dangers of love.

David is Rachel's husband. Like his wife, he has been successfully cured and embodies the calm, compliant adult behavior expected by their strict society.

Thomas is a boy who shared a connection with Rachel before she underwent the cure. He later works as a guard at the government prison known as the Crypts.

Frank is a cruel and suspicious guard who monitors the most secure wing of the government's prison facility. He strictly adheres to regulations and views the prisoners with absolute contempt.