A village near the North Korean border echoes with the sounds of military artillery and North Korean propaganda. During summer vacation, a young brother and sister venture up a mountain to gather berries. Heavy rains a month ago have damaged the trees, created a large waterway down the hill, and scattered debris at the mouth of the river. Torn warnings of unexploded bombs and landmines lie near the old barracks along the mountain trail the children follow. Soon after, the siblings stumble upon a mysterious sphere with an unknown purpose.