Sarah is a contemporary American artist who flees to the small Irish village of Thornwood to escape the painful aftermath of a personal tragedy. She rents a restored thatched house called Butler's Cottage, where her unspoken grief manifests as panic attacks and a growing reliance on alcohol. Finding a 1910 diary hidden inside a hollow tree provides her with a welcome distraction and a quiet way to indirectly process her own sorrow.

Anna is an 18-year-old farm girl living in 1911 Thornwood who possesses a perceptive mind and a deep knowledge of local folklore. She mourns the loss of her older sister and secretly believes she was taken by fairies. When an American academic arrives to study local legends, she volunteers as his assistant in hopes that his research will help her uncover the truth about her sister.

Harold is an empathetic American anthropologist who visits Ireland in 1910 to study the local Fairy Faith. He uses meticulous, academic methods to record rural folktales, viewing them as vital cultural records rather than mere superstitions. He approaches the villagers with respect and quickly forms a highly productive partnership with his young local assistant.

George is the wealthy, aristocratic son of the English landowner who controls Thornwood House in 1911. He projects a charming, gentlemanly facade but harbors a deep sense of entitlement and a capacity for casual cruelty. His position in the Anglo-Irish gentry grants him immense power over the local working-class community.

Olivia is George's twin sister, living a deeply isolated life at the grand Thornwood House. She is openly hostile toward the local Irish villagers and views any crossing of class boundaries with pure contempt. Local legends about her family's cursed history surround her and her brother.

Oran is a local conservation officer in modern-day Thornwood and a single father raising his teenage daughter. He carries heavy grief following the sudden death of his wife, making him fiercely protective of his family and the local environment. He cannot bring himself to enter his former home, Butler's Cottage, due to painful memories.

Hazel is Oran's perceptive teenage daughter, who possesses a strong interest in local supernatural lore. She reads books about fairy legends to maintain a connection to her deceased mother and acts as a bridge between the village's history and its present visitors.

Brian is a practical, reserved farmer who serves as Sarah's landlord in 2010. He maintains the historic properties in the village and possesses a long memory of the local families and their complicated histories.

Jack is Sarah's estranged husband, who remains in New York while she flees to Ireland. Their marriage has severely fractured under the weight of an unspoken tragedy, leaving them unable to communicate effectively about their shared pain.

Joe is Anna's father, a hardworking Irish farmer in 1910 who is highly protective of his family. He relies on traditional ways of living and initially views the American academic's presence with skepticism before warming to his polite demeanor.

Kitty is Anna's mother, a woman with roots in Dublin who desires a broader life for her children than the farm can offer. She recognizes her daughter's intelligence and actively encourages her to take the opportunity to work with Harold.

Paddy is Anna's older brother, a politically engaged young man with quiet ties to the Irish Republican Brotherhood. He is highly protective of his siblings and deeply invested in the growing movement for Irish independence from British rule.

Tess is Anna's close friend in the village, a young woman highly skilled in lace-making. She provides Anna with companionship, local gossip, and practical help in preparing for rare social events in 1911 Thornwood.

Maggie is a local seeress living on the fringes of 1910 Thornwood society. She is one of the few villagers who takes Anna's belief about her sister seriously and holds dark, long-kept secrets regarding the history of the Hawley family.

Ned is a modern-day traditional Irish storyteller known as the Fairy Whisperer. He actively preserves local folklore and leads environmental protests to protect sacred natural sites from modern development.

Marcus is a helpful hotel manager who goes out of his way to assist Sarah when she arrives in Ireland with nowhere to stay. He connects her with the Thornwood community and ensures she feels welcome.

Fee is Marcus's partner, a warm and pragmatic woman who lives on a farm near the famous hawthorn tree. She possesses a deep knowledge of traditional herbal remedies and acts as a grounding presence for weary visitors.

Milly is Anna's deceased older sister. Her mysterious death years prior fractured the family, leaving Anna with a lingering belief that she was taken by the fairies and might still be found in the invisible world.

Lord Hawley is the wealthy English patriarch who built Thornwood House in the 1880s. His arrogant dismissal of local folklore and destruction of a fairy tree supposedly brought a lasting curse upon his lineage.

Lady Hawley is the late mother of George and Olivia. She became convinced that her children were changelings left by fairies, a belief that led to her tragic death and cemented the local superstitions surrounding her family.

Danny is a member of the Irish Republican Brotherhood and a friend of Paddy Butler. He frequently hides from the local authorities while planning political actions against British rule in Ireland.