Ella is a florist in her forties who runs an independent flower shop in Devon specializing in a shabby-chic style. While traveling to London, she overhears two young men discussing their recent release from prison with two teenage girls. She decides against intervening or calling the girls' parents, a choice that consumes her with guilt when one of the girls disappears the following day. Ella is highly self-aware and critical of her own actions, often worrying about her physical appearance, her business, and her capabilities as a mother.

Henry is a farmer in his forties who lives on the sprawling Cornwall estate he inherited from his parents. To make ends meet, he operates holiday rental cabins on the land. Following the disappearance of his youngest daughter, Henry becomes withdrawn and consumed by grief, preferring the company of his animals and the routine of farmwork over social interaction. He keeps secrets from the police regarding his exact whereabouts on the night of the disappearance.

Sarah is a 17-year-old student from a modest background who excels academically. She traveled to London with her best friend Anna to celebrate the end of their secondary school exams. Sarah hides information from the police about the night Anna vanished, driven by fear of judgment and her own complicated trauma. She frequently experiences cruel bullying at school regarding her sexual behavior.

Matthew is a private investigator in his thirties and a former police officer. He left the force following a tragic incident involving a young suspect, an event that left him with physical scars and lasting guilt. As he anticipates the birth of his first child, Matthew brings a heightened sense of empathy and meticulous observation skills to his investigative work, often noticing details traditional police overlook.

Anna is a beautiful, talented 16-year-old girl who goes missing after visiting a London nightclub. She is passionate about musical theater and recently landed a lead role in a school production. Raised on a comfortable farm, she possesses a trusting nature and a strong sense of independence, though she is currently angry with her father over a family secret.

Tim is a 19-year-old from a working-class single-parent household on the local council estate. He frequently spends time at the Ballard farm, finding a sense of belonging in their bustling, prosperous home. Like Sarah, he looks up to the Ballard family and considers himself a close confidant of the sisters.

Barbara is Anna and Jenny's mother and Henry's wife. She is highly protective of her children and deeply resents Ella Longfield for failing to alert authorities on the train. As the anniversary of the disappearance approaches, Barbara channels her intense grief into organizing a community vigil to maintain hope.

Jenny is Anna's 18-year-old sister. She and Anna are remarkably close, separated in age by only a year and a half, and they share the same core group of friends. Jenny carries her own quiet guilt for backing out of the London trip at the last minute.

Tony is Ella's husband and Luke's father. He is practical and protective, frequently frustrated by the police's slow response to the threats against his wife. He works away from home occasionally but remains dedicated to his family's safety.

Luke is Ella and Tony's 17-year-old son. Generally considered an easy, unfussy child, he surprises his parents when he finds himself involved in a serious situation with his classmate. He is an avid hiker who previously completed the demanding Ten Tors challenge.

Karl is a young man recently released from prison. He and his friend Antony meet Anna and Sarah on the train and make plans to reconnect at a nightclub. His sensible advice to the girls about staying safe in London briefly reassures Ella before she learns of his criminal record.

Antony is a young ex-convict who engages with the teenage girls on the train. He slips away to the café car with Sarah during the journey, triggering Ella's concern for the girls' safety.

Bob is Sarah and Lily's estranged father. He was in London for work on the night Anna disappeared and sent Sarah a text message inviting the girls to his swanky hotel. His past behavior caused a deep rift in his family, leading to his divorce and estrangement from his daughters.

Margaret is Sarah and Lily's mother. She is emotionally distant from her daughters and stubbornly refuses to acknowledge their complaints about their father. She blames her older daughter, Lily, for the collapse of her marriage.

Lily is Sarah's older sister who left home after giving her parents an ultimatum regarding her father's behavior. She now lives in a religious commune, wears voluminous clothing and bracelets to hide past scars, and goes by the name Saffron.

Melanie is a police officer and former colleague of Matthew Hill. She often provides him with unofficial updates on investigations while simultaneously chiding him for leaving the force. She is sympathetic but frequently constrained by bureaucratic superiors.

Sally is Matthew's heavily pregnant wife. Following the birth of their daughter, Amelie, she acts as a sounding board for Matthew's theories about the case, utilizing her own keen observations about people to help him notice crucial details.

April is a local single mother living on the council estate. She is often busy and lacks the time to cook elaborate meals for her son, Tim, which leads him to seek comfort at the Ballard farm. She is quietly involved with someone in the community.

Emily is Luke Longfield's 17-year-old classmate. She experiences an unexpected life event that forces both her family and Luke's to sit down and discuss their futures, prompting Ella to reflect on her own biases.

Rebecca is Emily's mother. She is terse and protective, taking a direct approach to handling the sudden crisis involving her teenage daughter and Luke Longfield.

Paul is a member of Jenny and Anna's social circle. He originally planned to go on the London trip but dropped out, a decision that leads to intense infighting among the friends regarding who is responsible for leaving Anna vulnerable.

Caroline is the owner of the house and commune where Lily resides. She provides a structured, safe environment for young women in crisis, maintaining strict house rules to ensure their well-being.

Moon is a large man who lives at the commune with Lily. He is highly protective of her and actively tries to prevent Sarah from discussing past family trauma, knowing it causes Lily emotional distress.

The unnamed Detective Inspector from London is assigned as the lead investigator on Anna's disappearance. He is characterized by his aggressive interrogation tactics and his tendency to ignore local officers' advice.