Koo Gum is set during World War II when the Japanese Empire sent troops to Siam as part of their greater plan. Kobori, an idealistic Japanese officer set up a base camp by the Chaophraya River which is in the area of Angsumalin‘s house. He falls for her at first sight. Angsumalin, a proud Thai who despises every kind of threat to her country, sees him as a part of the Japanese Empire that deserves only hatreds. Despite his duty, Kobori wants to believe that his love will be able to find its way into her heart.