Ariadna discovers that her grandfather has been searching for the remains of her father, who disappeared during the Civil War. Determined to help him, she travels to Burgos, where a mass grave is being excavated, and where he could be buried. During her stay there, she will learn the story of Antoni Benaiges, a young teacher from Tarragona who was her grandfather's teacher before the war. Through an innovative pedagogical method, Antoni inspired his students and made them a promise: to take them to see the sea.