141 people from MacKay Presbyterian Church served in the First World War, and their church and their families at home steadfastly supported the war through four years of privation, suffering, and grief. MacKay church served New Edinburgh, a community with roots in the lumber industries at the Rideau Falls, which contained Rideau Hall and was home to a growing number of public servants and a large German-speaking minority, and had a rich tradition of athletics and militia service. MacKay church embraced the conviction that an immanent God was working in history, and that Christians had a duty to realize the Kingdom of God on Earth through evangelism and social and moral reform. They regarded the British Empire as the apogee of Christian civilization bringing peace and progress to the world. They were thus convinced that in defending their country and Empire against German aggression and autocracy they were fighting for “justice, truth, and righteousness, and for the Glory of God”. This study weaves together the stories of the men who served, their families at home, and their church as they responded to a terrible war. It focusses particularly on the nineteen men who fell in the war – some as heroes in desperate battles; others with tragic randomness or from illness; several with no known graves – as well as their siblings who also served, the widows they left to cope as best they could, the children who would grow up without fathers, and the families whose pride in their sacrifice was mixed with heartbreak at their loss; and it uses these stories to illustrate and develop the main themes of the book. Final chapters describe the return of the survivors and their adjustment, with their families, to a changed world, as they launched new careers or returned to old jobs, started new families, and in some cases struggled with permanent injuries and painful memories. MacKay Presbyterian Church became MacKay United Church, re-affirming its Christian faith and remembering those who had made the Supreme Sacrifice. This study of a church at war deepens our understanding of the social history of Canada’s response to the First World War, using new methods, including on-line research and the tools of genealogical study, to bring to life, however imperfectly, people who did not leave a rich legacy of information on their lives and families.