The search for documentation about the sea for a school work will make the magic door of Doraemon open and take Nobita to Shizuka, Gian and Sueno in the deep ocean. This time our friends embark on a huge and unique boat in order to learn about the mysteries of the sea and look for treasures. What nobody imagines is that a distortion in the line of space-time will lead them to the seventeenth century amid a great storm that will make them wreck and where Doraemon loses its magic pocket. No time to lose, our friends must find a way out. Will they succeed?