Young peer and junior member of the Foreign Office Mark St. Neots (John Justin) is obsessed with the memory of Sylvia (Moira Shearer), a 16-year-old redhead he met at a party as a boy, and vowed he would love forever. Now older and respectably married, Mark still retains his image of the beautiful young girl with the red hair, and spends the rest of his life searching for her, through a string of casual affairs.