Milly is a seventeen-year-old prep school student from New York with a sharp mind. Named after her estranged grandmother, she struggles with feelings of inadequacy due to her mother's high expectations and emotional distance. She agrees to spend the summer on Gull Cove Island in hopes of earning her mother's approval and a promised diamond necklace.

Aubrey is an athletic, freckled high school competitive swimmer from Oregon. She has spent her life trying to please her arrogant father, Adam, but recently learned a family secret that shatters her idolization of him. Preferring to avoid conflict, she eagerly accepts the invitation to Gull Cove Island to escape the tension at home.

Jonah is a teenager who travels to Gull Cove Island alongside Milly and Aubrey, claiming the spot of Anders's son. Harboring a deep resentment toward the wealthy elite, he carries a hidden agenda regarding his presence at the resort. He studies the people around him closely and maintains a guarded, slightly cynical exterior.

Mildred is the wealthy, elegant matriarch of the Story family who suddenly disowned her four children twenty-four years ago. She resides permanently on Gull Cove Island in her heavily guarded estate, Catmint House. Now a recluse, she communicates primarily through her lawyer and assistant, maintaining tight control over the family wealth and legacy.

Allison is the only daughter in the Story family. She lives in New York and maintains a highly critical, emotionally distant relationship with her own daughter. Deeply affected by her mother's abrupt rejection twenty-four years ago, she views the summer invitation as a rare opportunity to mend the fractured family dynamic.

Adam is Aubrey's father and the former "golden boy" athlete of the Story family. He grew up believing in his own greatness and superiority but has settled into a life as a moderately successful author. His recent selfish decisions have severely damaged his marriage and his relationship with his daughter.

Anders is one of the Story siblings, known for his cutthroat behavior and financial mismanagement. He has a reputation for offering bad investment advice that ruins his clients, yet he routinely shifts the blame to others. Like his brother Adam, he prioritizes money, reputation, and his own success above all else.

Archer is the youngest of the four Story siblings. During his youth, he struggled with substance abuse and often felt out of place among his more aggressive and self-assured older brothers. He carries the emotional weight of his family's dysfunction and eventually attempts to seek genuine connection away from the toxic estate.

Theresa is Mildred Story's faithful assistant who manages the day-to-day operations at Catmint House. Following the death of Abraham Story, she moves into the family home to be closer to her employer. She acts as the primary gatekeeper for the reclusive matriarch, filtering all communication and visitors.

Donald is the powerful lawyer for the Story family estate. He was responsible for delivering the cryptic letter that disinherited the Story children twenty-four years ago. He is highly protective of Mildred's privacy and actively attempts to bribe the visiting teenagers to leave Gull Cove Island immediately upon their arrival.

Matt is Theresa's son, described as a charming local boy who is unpopular with the wealthy Story brothers. During the summer of 1996, he views his interactions with the affluent summer residents as casual, entirely unaware of the severe consequences his presence brings to the image-conscious family.

Dr. Baxter is the elderly former family doctor for the Storys. He wanders Gull Cove Island appearing confused and suffering from memory issues. However, his timely interruptions during conversations about the Story family's past suggest he retains a sharper mind than he lets on.

Hazel is a local islander and Dr. Baxter's granddaughter. She is highly curious about the famous Story family and acts as a local historian, sharing the island's many rumors about why the siblings were exiled from Gull Cove Island.

Kayla is a local girl from the summer of 1996 who previously dated Anders Story. Her decision to move on and date Matt Ryan creates intense friction with the prideful Story brothers, making her a target of their anger and a central figure in the island's past tragedies.

Oona is the owner of a local clothing boutique named after her late sister, Kayla. She helps Aubrey find confidence in her appearance and provides the teenagers with crucial historical context about her sister's connection to the Story family twenty-four years ago.

Abraham is the late husband of Mildred and the founder of the family's immense wealth on Gull Cove Island. His personal motto regarding family loyalty deeply influenced his children, though they interpreted his words in vastly different, often toxic ways.

JT is Anders Story's real son and a true grandchild of Mildred. Uninterested in working a minimum-wage summer job for an estranged relative, he orchestrates a secret arrangement with a classmate to take his place on Gull Cove Island.