The theme of The Sparrow is the conflict presented to Ralph Kimberley, a London vicar, by his ardent support of the Campaign for Nuclear Disarmament. Although a kind, well-intentioned man, he does not realise the effect his sympathies are having on his parish, nor on those who are close to him.
His wife, Myra, feels neglected and unloved and finds herself taking an unhealthy interest in Keith Wilson, a young discharged prisoner whom Ralph has befriended. His orphaned niece, Sarah, too, feels herself alone and unwanted.
It takes dramatic events to bring home to Ralph the knowledge that his personal obligations must come before his devotion to the cause. Instead of choosing the role of a martyr, he must perform an act of apparent cowardice to begin a fresh start.