Mary Jane is a quiet, obedient 14-year-old girl who lives with her conservative, upper-middle-class parents. She sings in her church choir and follows her mother's strict rules regarding cooking and household management. Accustomed to a highly orderly and emotionally restrained environment, she finds herself curious about the chaotic but affectionate household where she begins nannying. She is highly observant and possesses a natural talent for culinary tasks and musical harmonies.

Jimmy is a rock musician in his thirties and the lead singer of the band Running Water. He is staying at the Cone residence for the summer to receive psychiatric treatment for his drug addiction in secret. Despite his fame and bad-boy image, he displays a kind, charismatic personality and struggles deeply with the pressures of celebrity life, using substances to numb his anxiety around public adoration.

Sheba is a beautiful, famous television star and former child actress who is spending the summer in hiding at the Cone house to support her husband's recovery. Despite her celebrity status and glamorous appearance, she is highly approachable and readily helps out around the house. She carries emotional baggage from an abusive childhood where her mother pushed her into show business and favored her brothers.

Dr. Cone is a psychiatrist specializing in addiction therapy who runs a practice from his home office in Roland Park. A former college rock band guitarist, he maintains an open, friendly demeanor but approaches his household with a level of emotional detachment. He brings high-profile clients into his home for intensive, secretive treatment while allowing his own house to fall into total disarray.

Bonnie is a red-haired, flamboyant woman who approaches life with a slapdash, freewheeling attitude. As a doctor's wife living in a wealthy suburb, she resents her conventional domestic role and completely neglects household chores like cooking and cleaning. She acts more like an aging flower child who wishes for a life filled with excitement, music, and glamour.

Izzy is the five-year-old daughter of Richard and Bonnie Cone. Raised in a household with no strict rules or boundaries, she is highly imaginative, effervescent, and fiercely independent. She quickly forms a strong attachment to her new nanny, introducing Mary Jane to open expressions of affection and joining her as an eager assistant in the kitchen.

Mrs. Dillard is an attractive, conservative blonde woman living in Roland Park. She places an overwhelming emphasis on social status, neatness, and the opinions of her country club neighbors. A strict Presbyterian, she teaches Sunday school and tightly controls her daughter's life, preventing Mary Jane from taking on unsupervised responsibilities in the kitchen or elsewhere.

Mr. Dillard is a conservative lawyer who lives a highly structured life in Roland Park. Emotionally distant and rigidly polite, he takes little interest in his daughter's daily life or domestic matters, preferring his golf games at the Elkridge Country Club. He holds strong prejudices against anyone outside his immediate social, racial, and religious demographic.

Beanie is a new neighbor in the Roland Park community who shares the Dillard family's emphasis on appearances and social pretensions. She is highly nosy and harbors a persistent, secretive fascination with the famous guests staying at the Cone residence, often creating excuses to drop by uninvited to spy on them.