Lucy is a 20-year-old journalism student at Hamilton Hume University. She manages a rare skin condition called aquagenic urticaria, which causes an allergic reaction to water. After a classmate shares a private photo of her online, she faces a formal complaint and public humiliation. Seeking a safe haven and answers to her vivid dreams about a historical shipwreck, she drives to her sister's house in Comber Bay.

Jess is a painter preparing for an upcoming art exhibition titled The Sirens. She lives an isolated life at Cliff House in Comber Bay, wearing dark clothing to conceal the same water allergy that affects her sister. As a teenager, her feelings of alienation led her to investigate her origins, eventually discovering she was the abandoned infant known locally as Baby Hope.

Mary is a 16-year-old Irish girl transported aboard the convict ship Naiad. After a rent collector attacked her by a stream, her sister intervened, resulting in criminal sentences for both girls. Mary grieves the long-ago disappearance of her mother and fears the ocean, but she works to build a supportive circle among the imprisoned women to survive the harsh voyage.

Cameron is a young art teacher who gives Jess extra attention and painting lessons during her high school years. He represents the first person outside of Jess's family who makes her feel appreciated for her differences. His inappropriate focus on a teenage student introduces a dangerous dynamic into her life.

Eliza is Mary's blind twin sister, sentenced to transport to New South Wales after striking a man with a rock to stop him from assaulting Mary. She relies on her sister to describe their surroundings on the ship but possesses a sharp intuition. She remembers their mother's legends about the sea clearly and helps Mary face their daunting reality.

Robert is a fisherman in the Comber Bay area who discovered an abandoned infant in a sea cave in 1982. He adopted the child with his wife, prioritizing his family's safety and well-being. He provides a nurturing, protective presence for his daughters, making significant personal sacrifices to ensure they grow up in a loving environment.

Judith is Robert's wife and a fiercely protective mother who alters her life to safeguard her family. When local gossip and tabloid attention threaten their peace after adopting an infant found in a cave, she willingly uproots her life. She maintains a stable home for her children despite occasional emotional distances.

Max is a gentle young man who has been Jess's best friend since they were five years old. He accepts her without judgment and provides a safe space for her to express her fears about her family and her health condition. He offers loyal companionship during her isolating teenage years.

Melody is a Comber Bay resident of Wiradjuri heritage who watches over Jess's home. She believes the local bay actively protects women and shares local legends with Lucy. Despite living in the area for years, she still feels like an outsider, which helps her bond with the visiting sisters.

Ben is a college student at Hamilton Hume University who has a brief romantic encounter with Lucy. He violates her trust by sharing a private photograph of her online without consent. When reported, he avoids consequences, forcing Lucy to leave school.

Bridie is a resourceful, red-haired convict imprisoned aboard the Naiad. She makes difficult choices to survive the voyage, including trading favors with sailors to secure extra food. Despite harsh judgments from others, she shares her rations to help her fellow prisoners.

Sarah is an imprisoned woman traveling on the Naiad alongside her young daughter, Annie. She was convicted of stealing after refusing the advances of a man. She works closely with Mary and Bridie to endure the harsh conditions in the ship's hold.

Aoife is an older Irish woman on the convict ship who was sentenced for murdering her abusive husband. She demonstrates remarkable solidarity with the younger women aboard the Naiad, ultimately taking the blame and harsh punishment for a group infraction to protect them.

Byrne is a rent collector for a Protestant landlord in Ireland. His violent assault on Mary by a stream sets off the chain of events that leads to the sisters' imprisonment and transport to Australia.

Da is Mary and Eliza's father, a fisherman who became a weaver to raise his daughters inland after his wife disappeared. He represents a gentle, protective model of masculinity and provides a loving home for the twins before their arrest.

Mam is Mary and Eliza's mother who disappeared into the sea when the twins were five years old. According to local legend, she was a merrow, an Irish mermaid, whose stories and sudden absence deeply influence her daughters' lives.

The Captain commands the transport ship Naiad. He subjects the imprisoned women to cruel conditions, severely limiting their food and water rations during the long voyage to New South Wales.

Annie is Sarah's young daughter, traveling with her mother in the dark hold of the Naiad. The other women pool their limited resources to ensure she receives enough food to survive the journey.

Daniel is a local Comber Bay resident and one of the missing men known locally as the Eight. Before his disappearance, he took Melody to a sea cave and attempted to assault her, but was deterred by the mysterious sound of women singing.

Ryan is Daniel's brother, who sits near the local monument commemorating the Naiad shipwreck. He speaks with Lucy about the area's history and provides a file of research his father compiled about the doomed ship.