Complex sentence: The story line was a soldier is receiving a letter from his beloved girl written on the back of her picture, but before he had the time to read it, the strong desert wind is carying it to the other side of the border.
Split into simpler sentences: The story line was about a soldier is receiving a letter from his beloved girl written on the back of her picture. However, before he has the time to read it, the strong desert wind carries it to the other side of the border.