Year of 1969, after drawing an unlucky number from a lottery result, Pao from southern Taiwan has to serve the military in the remote and perilous island of Kinmen which is seen as the most dangerous military base due to its geographical location that is too close to China. Pao is assigned to the Sea Dragon, a unit known for having the toughest physical training. However, Pao is about to find out that that the greatest challenge in his military service is not in the Sea Dragon but lies in Unit 831, a special task he is later appointed to.
