Grace is a 72-year-old retired mathematics teacher living in Lincolnshire, England. She spends her days living quietly and grieving the deaths of her husband and son. Her stagnant routine is interrupted when she receives a solicitor's letter stating she has inherited a house in Ibiza from a former colleague. Despite feeling too old for such a trip, she makes the impulsive decision to travel to the island, where she encounters strange phenomena that challenge her strictly logical worldview.

Alberto is an elderly marine biologist who runs a diving company called Atlantis Scuba in Ibiza. He has an unkempt, castaway-like appearance with youthful eyes and a deep knowledge of the local marine environment. He serves as an eccentric guide to Grace when she arrives on the island, promising to show her the truth about Christina's life. He maintains a deep connection to the island's mysterious environmental elements.

Christina is Grace's former colleague who left her teaching career to pursue singing in Ibiza. She is a mysterious figure who legally leaves her Ibiza house to Grace under unresolved circumstances. Prior to her disappearance, she offered psychic services at a local market and passionately opposed luxury developments on the island.

Art is an English real estate mogul and the owner of Eighth Wonder. He plans to build a luxury resort on Es Vedrà, a fragile rock formation off the coast of Ibiza. His relentless pursuit of profit puts him at direct odds with the local activists and environmentalists on the island who want to preserve the local habitats.

Maurice is a 22-year-old university student finishing his mathematics degree. He recently lost his mother and feels stuck in a pattern of depression and grief. He contacts Grace because he remembers her past kindness, prompting her to write down the story of her time in Ibiza for his benefit.

Marta is Alberto's daughter and a dedicated environmental activist in Ibiza. She is highly motivated to protect the island from luxury developments and organizes major protests against Eighth Wonder. She is intelligent, well-spoken, and deeply committed to continuing Christina's conservation efforts.

Daniel is Grace and Karl's late son. He died in 1992 at a young age when he was struck by a truck while riding his bicycle in the rain. His death is the central tragedy of Grace's life, and her memories of him heavily influence her present-day choices and self-worth.

Karl is Grace's late husband, who passed away four years before the events of the story. His death compounded Grace's long-standing grief over their son. Though he is gone, Grace frequently speaks to him in her mind and struggles with guilt regarding their complicated marital history.

Lieke is Christina's daughter, working as a famous singer and DJ who frequently performs at the local Amnesia nightclub. She has a strained and complicated history with her mother, creating tension when Grace reaches out to her.

Sofía is a powerful local politician in Ibiza. She holds the authority to approve or deny real estate developments on the island. She finds herself caught between the financial promises of foreign developers and the passionate protests of the local residents.