The Silver Sword realistically presents the problems of war as seen through the eyes of a Polish family torn apart by World War II. The novel's main characters include three children—Ruth, Edek, and Bronia Balicki—who are left to live as best they can in the streets of Warsaw when their father is sent to a prison camp and their mother is taken away to do forced labor in Germany. Serraillier explores the meaning of courage, unselfishness, loyalty, and honesty as the children try to survive in a world made brutal by war. Violence is never depicted graphically, however, and more than half the novel takes place immediately after the war. The hardships the children endure arise from the deprivations war imposes on all members of their society. The feelings of hatred that result from the war must be overcome in order to produce a society in which people from once-hostile countries can live together in peace.

Serraillier stresses that peaceful societies must be founded upon love and trust and demonstrates this theme most concretely in the relationship between Ruth, the model of "courage, self-sacrifice, and greatness of heart," and Jan, an orphan who has learned that he can survive and remain self-sufficient only by stealing. Ruth's love gradually brings Jan from a state of selfishness to one of loyalty and self-sacrifice. The Silver Sword is a story of hope and love in which the children undertake a journey of discovery in search of their parents that brings out the essential qualities in each of them.