In 1592, admiral Yi Sun-sin and his fleet face off against the might of the invading Japanese navy and its formidable warships. As the Korean forces fall into crisis, the admiral resorts to using his secret weapon, the dragon head ships known as geobukseon, in order to change the tide of this epic battle at sea.

The film mainly follows the famous 1597 Battle of Myeongryang during the Japanese invasion of Korea (1592-1598), where the iconic Joseon admiral Yi Sun-sin managed to destroy a total of 133 Japanese warships with only 13 ships remaining in his command. The battle, which took place in the Myeongryang Strait off the southwest coast of the Korean Peninsula, is considered one of the greatest victories of Yi.

13 years after the King Injo Revolt, the Chosun Dynasty is attacked by the Chung Dynasty of China. A young man named Na-mi leaves his demolished village to find his young sister, Ja-in, and her finance Su-koon, who were to wed on the very day of the attack. While on his mission to rescue her, he is being traced by Jushinta, a fierce Chung Warrior, and his band of malicious men who are out to stop him. Na-mi has but a day to rescue his sister before she is taken away to be a slave. When Na-mi finally finds his sister, Jushinta comes between them and a fierce battle between two of the finest warriors unfolds.