A 12-year-old Hayley Mills made her big-screen debut in this melodramatic thriller as Gillie, a young girl living in Cardiff. She accidentally witnesses a Polish sailor named Korchinsky shoot his girlfriend dead in a fit of rage after he finds out she's left him for another man. Gillie steals the murder weapon, and tries to get away. But Korchinsky succeeds in catching up with the little girl, with Investigating Officer Graham (John Mills) in hot pursuit, but finds that he just cannot harm the child. When the lonely duo form an unlikely bond, Gillie realises that she must mislead the police if she is to save her new-found friend.