Yeong-Su and Jeong-A have a friendship as high school students who attend school by train in K city. As their naive love grows, they promise their futures, making many problems in the schools where the friendship between boys and girls is prohibited strictly. After the training of the Student National Defense Corps, Young-Su goes to see Jeong-A, who died of a malignant pneumonia one day before. Recollecting the railway along which he walked with her, he decides to keep the lost story in his deep mind.