Ada is a 10-year-old girl born with a clubfoot. Her mother uses this physical condition to justify keeping her entirely isolated indoors. Uneducated and accustomed to severe physical and verbal abuse, she possesses a fierce determination to survive. When the threat of war prompts the evacuation of London's children, she seizes the opportunity to teach herself to walk and escape her confinement.

Mam is a single mother working night shifts at a London pub to support her children. Bitter and exhausted by her circumstances following her husband's death, she takes her frustrations out on Ada and Jamie. She is deeply ashamed of Ada's physical disability and forces her to live a completely isolated existence without basic education or proper medical care.

Jamie is Ada's six-year-old brother, a restless and undernourished boy preparing to start school. Unlike his sister, he is allowed outside the apartment and has some experience with the wider world. The trauma of his upbringing manifests in severe anxiety and a desperate desire for a stable home environment.

Susan is a single, university-educated woman living alone in a village in Kent. Grieving the death of her best friend Becky, she lives in a state of isolation and depression until the war forces her to take in evacuees. Despite her initial insistence that she is unfit to care for children, she quickly proves attentive to their physical and emotional needs.

Stephen is a neighborhood boy from London who evacuates to the same village in Kent. He provides early assistance to Ada when her foot bleeds during the walk to the train station. In Kent, he lives with a retired military officer and consistently extends friendly overtures to Ada.

Lady Thorton is a wealthy, authoritative figure in the village who organizes the Women's Volunteer Service and the billeting of evacuees. She is strict and commanding, single-handedly assigning Ada and Jamie to Susan's household when no one else chooses them.

Margaret is Lady Thorton's daughter, a privileged girl who attends boarding school. She shares Ada's love of horses and treats Ada as an equal, unbothered by her physical differences or lack of formal education.

Fred is the stable manager at the Thorton estate. He possesses extensive knowledge of horses and recognizes Ada's natural affinity for them. He steps in to provide the practical guidance Ada needs to care for Susan's neglected pony.

Dr. Graham is the village physician who provides the children's first proper medical assessments. He diagnoses their severe malnourishment and informs Susan that Ada's clubfoot is a condition that could have been surgically corrected in infancy.

The Colonel is an elderly, blind military veteran living in Kent. He takes Stephen in and repeatedly extends invitations to Ada to join them for tea, offering her a chance to practice social etiquette in a safe environment.

Becky was Susan's best friend who died of pneumonia three years prior to the story's start. Though absent, her legacy heavily influences the household, from the neglected pony in the yard to the packed-away sewing machine.

Butter is a bright yellow pony with a white stripe. Originally belonging to Becky, he has been unintentionally neglected by Susan. He becomes Ada's primary motivation for going outside and her vehicle for physical freedom.

Bovril is a stray cat that Jamie rescues and claims as his own. The cat serves as a source of comfort for Jamie, helping to ease his night terrors and anxiety.

Billy is Stephen's younger brother and a friend of Jamie's from London. His early return to the city triggers Jamie's homesickness.

Daisy is a publican's daughter who assists the Women's Volunteer Service when ships carrying wounded men from Dunkirk arrive. She helps keep Ada grounded during the overwhelming medical crisis.