Mallory is a 24-year-old aspiring literary professional who finds a new sense of purpose after relocating permanently to Nantucket Island. Leaving behind a receptionist job in New York, she embraces the slower pace and close-knit community of her newly inherited cottage. A free spirit who rebels against her mother's strict traditional expectations, she values her local connections and eventually finds profound fulfillment teaching high school English. She is caring, easy-going, and deeply loyal to her friends, preferring an unconventional but genuine life over societal expectations.

Jake is a pre-med student from South Bend, Indiana, taking classes to appease his doctor parents while secretly aspiring to work as a lobbyist in Washington D.C. He carries lasting grief over the childhood loss of his twin sister, an event that shapes his profound desire to find meaningful work related to cystic fibrosis. Family-oriented and intensely caring, he values deep interpersonal connections over prestigious titles or high-stress achievements. He tends to remain stubbornly loyal to his established commitments, sometimes avoiding necessary confrontations in favor of maintaining stability.

Ursula is an exceptionally driven, competitive, and high-achieving lawyer from South Bend, Indiana. Having bonded with Jake after showing kindness to his sick sister in middle school, she remains focused primarily on her career trajectory, status, and legal prestige. Her intense dedication to her professional life means she often expects her partner to adapt to her demanding schedule and frequent relocations. Emotionally reserved and intensely practical, she serves as a sharp personality contrast to those who prioritize personal warmth over professional achievement.

Leland is Mallory's wealthy, cosmopolitan, and highly competitive friend from New York. Used to having social and financial advantages, she operates with a sense of ambition that often dominates her friendship with Mallory. She rarely hesitates to pursue what she wants in her career at a prestigious literary magazine. She enjoys the status of being connected to high-profile individuals and tends to view relationships through a lens of influence. Her sophisticated exterior often masks deeper insecurities and an underlying jealousy regarding her personal connections.

Frazier is Cooper's best friend and an attendee at the fateful Labor Day bachelor party on Nantucket. Hard-working and entrepreneurial, he builds a business managing a chain of coffee shops in New England. Although he struggles with alcohol use during early social gatherings, he is fundamentally generous and maintains strong, enduring ties to his core group of friends. His shared history with both Cooper's family and Leland creates complex social dynamics during group gatherings.

Cooper is Mallory's older brother, a charismatic man whose numerous romantic entanglements keep him in a state of personal flux. He frequently relies on his sister's generosity, using her newly inherited Nantucket cottage as a gathering place for his fraternity friends. As a central social connector, he effortlessly bridges the gap between his college peers and his family members. Despite his romantic restlessness and occasional irresponsibility, he remains highly protective of his younger sister.

JD is a local first responder and volunteer firefighter on Nantucket who remembers Mallory from her early waitressing days. He is invested in building a relationship with her but often struggles with possessiveness.

Apple is a warm, supportive local resident on Nantucket Island who eventually works as a high school guidance counselor. She forms a close, nurturing friendship with Mallory, providing a grounded local connection.

Bayer is a wealthy, well-connected man who spends time sailing around Nantucket. He is involved in politics and enjoys a casual, whirlwind summer dynamic with Mallory, teaching her how to sail while he guards personal secrets closely.

Fifi is a celebrated, charismatic literary figure who meets Leland at a writers' workshop in Vermont. She uses her charm and status to manage social situations effortlessly, eventually moving in with Leland and altering the long-standing dynamic between Leland and Mallory.

Scott is a handsome, financially secure local businessman on Nantucket. Personable and open about wanting a long-term commitment, he treats his employees well and represents a stable romantic option for Mallory.

Greta is Mallory and Cooper's late aunt. She was estranged from most of her family after coming out as a lesbian following her husband's death, but maintained a bond with Mallory, ultimately leaving her a significant inheritance and a beloved Nantucket cottage.

Ruthie is Greta's long-term partner. Following Greta's death, she remains loosely connected to the Blessing family, eventually sharing holidays with them despite the family's past estrangement from Greta.

Link is Mallory's son, raised primarily on Nantucket Island. He grows up playing baseball and adjusting to the complexities of his unique family structure, bringing immense joy and a profound sense of purpose to his mother's life.

Bess is Ursula's daughter, raised in a demanding household where her mother's political ambitions take center stage. Jake is a highly devoted, hands-on father to her, and she grows up experiencing the pressures of her mother's high-profile career.

Anders is a driven legal professional who works closely with Ursula. Their intense working environment blurs professional boundaries, and he is characterized by his ambition and sudden relocations for work.

Kitty is Mallory and Cooper's mother. She holds strict, traditional ideas about femininity and propriety, which often puts her at odds with her more free-spirited daughter, though she remains an integral part of the family structure.

Mr. Blessing is Mallory and Cooper's father. He maintains a complicated personal life that occasionally disrupts the family's stability, but he shows immense enthusiasm for his grandchildren and family milestones.

Jessica is Jake's twin sister who died of cystic fibrosis at the age of thirteen. Her passing profoundly impacts Jake's life trajectory, guiding his career choices and anchoring his connection to Ursula, who showed Jessica kindness during her illness.

Tish is a woman who marries Cooper after a whirlwind romance. She attends Cooper's Nantucket wedding, where her presence inadvertently prompts questions about the group's recurring Labor Day weekends.

Hugo is a local Nantucket resident who becomes engaged to Apple. Their sudden marriage plans create unexpected scheduling complications for Mallory's social life.