Thirteen-year-old Rose Campbell is a recently orphaned heiress returning from a restrictive boarding school to await her new guardian. Raised in a sedentary and highly sheltered environment by her late father, she arrives at Aunt Hill feeling pale, sickly, and overwhelmed by her large extended family. Despite her initial timidity and fragile health, she possesses a naturally sharp intellect and responds eagerly to affection and practical education.

Alec Campbell is a seafaring doctor returning from overseas to assume guardianship of his orphaned niece. He actively rejects conventional 19th-century medical treatments and restrictive women's clothing, prescribing fresh air, loose garments, and physical exercise instead. He takes his moral and familial obligations very seriously and aims to build robust physical health as a foundation for strong character.

Phebe is a fifteen-year-old servant working at the Aunt Hill estate. Having grown up in the poorhouse after being abandoned as an infant, she is accustomed to difficult physical labor but remains exceptionally resilient and gracious. She looks upon Rose's wealthy lifestyle with wide-eyed admiration and quickly becomes a devoted companion.

Aunt Jessie is the mother to four of the boy cousins and acts as the most emotionally intuitive woman in the Campbell family. She prioritizes open communication with her children, often giving them gentle moral counsel rather than harsh discipline. She wholeheartedly supports Alec's unorthodox child-rearing methods.

Archie is the eldest of the seven cousins, acting as the "Chief" and informal leader among the boys. He is a thoughtful, respectable young man with a strong moral compass. He takes his responsibilities as the oldest brother seriously, often stepping in to mediate disputes or set a good example.

Mac is a deeply studious, introverted cousin who ruins his eyesight by constantly reading in poor lighting. He appears somewhat awkward socially but possesses a genuine curiosity about geology and science. Forced into a dark room to recover his vision, he learns to appreciate the comfort and company of others.

Known as "Prince Charlie," he is the confident, attractive son of Aunt Clara. He is popular and outgoing but occasionally weak-willed, easily swayed by peers into participating in ungentlemanly habits like smoking and gambling.

Aunt Plenty is a practical, energetic great-aunt who thrives on the daily responsibilities of running a large household. She is a bustling domestic powerhouse who finds deep satisfaction in traditional homemaking skills and practical chores.

Aunt Peace is a gentle, silver-haired great-aunt whose betrothed died on their wedding day years ago. She maintains a serene, melancholic presence in the house and excels at fine needlework, which she passes on to the younger generation.

Aunt Jane is a diligent housekeeper who values strict academic learning. Her intense focus on daily household tasks sometimes distracts her from providing emotional support and moral guidance to her own children.

Aunt Clara is a socially ambitious woman deeply concerned with high society and high fashion. She frequently clashes with Uncle Alec over his preference for loose, practical clothing, preferring garments that mold a woman to the current style regardless of comfort.

Aunt Myra is a nervous, deeply pessimistic woman who suffered the tragic loss of her own daughter. She relies heavily on unapproved medicines and views robust physical activity with intense squeamishness and suspicion.

Uncle Mac is a commercially successful shipping merchant who brings back exotic goods and international associates from his travels. At home, he remains extremely quiet and entirely defers to his wife's authority over the domestic sphere.

Uncle Jem is a jovial sea captain whose career frequently keeps him away from Aunt Hill. Despite his long absences, he possesses a tender heart and immediately recognizes the familial resemblance in his newly orphaned niece.

Steve is a fashionable young gentleman often referred to as "Steve the Dandy." He pays close attention to his clothing and social standing, occasionally finding himself needing financial assistance due to minor debts.

Will is one of Aunt Jessie's energetic middle sons. He loves reading sensational adventure novels filled with shallow heroes, a habit his mother works to correct by encouraging more wholesome literature.

Geordie is another active son of Aunt Jessie. Like his brother Will, he enjoys boisterous play and thrilling novels, though he is ultimately cooperative and willing to improve his habits for the sake of family harmony.

Jamie is the youngest of the boy cousins, an energetic toddler who clings affectionately to his mother. He loves playing imaginary games in the woods and provides lighthearted, chaotic energy to the family gatherings.

George was Rose's father, an invalid who lived a highly sheltered, sedentary lifestyle. His poor health limited his social circles and traveling, an approach that left his daughter physically weak and deeply grief-stricken upon his passing.

Ariadne is a haughty young woman from a respectable local family. She visits Rose out of a desire for social status rather than genuine friendship, using her time to show off her new jewelry and pressure Rose into making superficial decisions.

Fun See is a Chinese businessman working with the Campbell shipping operation. He presents a cultural contrast to the sheltered Campbell family and kindly gifts Rose an ornate fan during their meeting.

Mr. Whang Lo is a Chinese merchant who meets the Campbell family aboard their ship. He politely shares imported tea with his hosts and gives Rose a beautiful Chinese umbrella.

Pokey is a curious four-year-old girl who frequently tags along with young Jamie. Small and occasionally mischievous, she happily participates in the children's outdoor games and woodland adventures.

Debby is the grumpy, practical cook employed at the Aunt Hill estate. She focuses strictly on her culinary duties and enforces the aunts' schedules, showing little patience for interruptions in the kitchen.

Mother Atkinson is a host at Cosey Corner, a rustic homestead in the mountains of Portland, Maine. She provides a welcoming, outdoorsy environment where Rose and Mac can recover their health.

Father Atkinson runs Cosey Corner alongside his wife. He helps arrange the large picnic on Mount Windy-Top to celebrate Rose's birthday.