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.

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.

In the winter of 1598, the seven-year Imjin War nears an end as the Japanese Wae invaders prepare to withdraw from Joseon. Admiral Yi Sun-shin leads an allied fleet of Joseon and Ming ships to annihilate the Wae army. Joseon, Ming, and Wae forces clash at Noryang Strait, the deadly sea where Admiral Yi fights his last valiant battle.