Rowan is a middle-aged former carpenter who built her own home in the Australian Outback before a massive brush fire destroyed it. She travels to isolated Shearwater Island searching for her husband, Hank, who took a job there as a botanist. Having lost her brother to drowning at a young age, she holds others at a distance and maintains a highly pessimistic outlook on the environment's future.

Dominic serves as the caretaker and handyman of the Shearwater Island Seed Vault. He moved to the isolated, stormy island with his three children after his wife passed away during childbirth. Highly disciplined and technically skilled at repairing broken infrastructure, he struggles to express his emotions verbally and carries immense grief regarding his wife's passing.

Raff is the 18-year-old eldest child of the Salt family. He has a learning disability and works from a ninth-grade textbook, but he is a gifted musician who records underwater whale sounds to pair with his violin playing. He struggles to manage intense feelings of anger and grief, heavily relying on a physical outlet to work out his frustration.

Fen is Dominic's 17-year-old daughter. She is an independent, spirited teenager who chooses to sleep in a boathouse on the beach rather than inside the family lighthouse. She spends hours swimming with the island's native seal population and feels completely comfortable with the ghosts and spirits she believes inhabit the island.

Orly is the nine-year-old youngest child of the Salt family. He possesses an encyclopedic knowledge of botany and the specific survival mechanisms of the seeds stored in the island's vault. Highly empathetic to the natural world, he believes he can hear the voices of animals in the wind and insists on prioritizing the survival of plants that feed wildlife over human crops.

Hank is a senior botanist and Rowan's husband. Following the destruction of his home in the Outback, he accepts a position managing the Shearwater Island Seed Vault. His work requires him to shoulder the immense psychological burden of determining which plant species will be saved from rising sea levels and which will be left to go extinct.

Claire is Dominic's late wife and the mother of Raff, Fen, and Orly. She passed away while giving birth to Orly, having made the difficult choice to forgo cancer treatment during her pregnancy to ensure her child's survival.

Alex is a scientist who came to Shearwater Island to study seals. He is much less experienced than the other researchers, which makes him feel isolated until he forms a strong romantic connection with Raff.

Tom is a climate change scientist studying extreme weather on Shearwater Island. He is Alex's older brother and closely monitors the dangerous storms that frequently hit the isolated area.

Naija is Tom's girlfriend and a member of the scientific research team previously stationed on Shearwater Island. She faces the dangerous island storms alongside her partner.

River is Rowan's late younger brother. He drowned during their childhood while living on a houseboat, a tragic event that deeply affects Rowan's views on family, guilt, and safety.