A ten-year-old girl, Ada Smith, lives in London with her mother and younger brother, Jamie. Her father passed away when she was just six years old. Ada has a physical deformity called clubfoot, which hinders her ability to walk. Her mother, an abusive and neglectful woman, feels embarrassed by Ada's impairment, preventing her from going outside or playing with other kids. Despite handling household chores and taking care of Jamie, Ada endures her mother's harsh punishments and abusive behavior.
After World War 2 begins, the British government orders children to move to the countryside for safety, but Ada's mother refuses to let her kids go. Despite her mother's opposition, Ada secretly leaves with Jamie, reaching Kent, where they meet their foster guardian, Susan. Initially reluctant, Susan gradually becomes closer to Ada, encouraging her to learn empowering skills. Ada learns to walk with crutches, rides horses, and becomes a confident girl who assists villagers and detains a spy. When Ada's mother gets a letter from Kent, she takes her children back to London.
After Ada returns to London, her mother confiscates her crutches and prohibits her from leaving the house. Ada's disappointment intensifies when she discovers that her mother took them back solely for the child support money from the government. Despite the mistreatment, Ada remains hopeful and plans to escape again. Ada and Jamie survive a bomb attack, taking shelter where they reunite with Susan, who comes in search of them. Ada realizes Susan's selfless act towards them and pledges to repay her kindness by becoming a strong girl.
