Aidan MacCarthy, an Irish doctor serving with the RAF, survived a Japanese POW camp and was present in Nagasaki when the atomic bomb fell in 1945. He helped treat the wounded in the aftermath, and a Japanese officer later gave him a samurai sword in gratitude for the lives he saved. The film follows MacCarthy's son and grandson decades later as they trace that sword back to Japan, tracking down the family of the officer who gave it and piecing together what happened between the two men amid the ruins of the city. Wartime photographs, POW camp records, and interviews with historians and family members reconstruct MacCarthy's ordeal, from imprisonment and forced labor to a shipwreck survival and finally the bombing itself. The search for the sword's origin becomes a way of tracing an unlikely connection between an Irish doctor and a Japanese soldier, forged in one of the war's most devastating moments, and of understanding what a single object can carry across generations and continents.