Rampant

Lee Chung, Prince Gangrim, comes back to Chosun to fulfill his dead brother’s last will. Arriving at Incheon, however, he finds out monstrous creatures called "Night Demon" are rampant in the area. He accompanied one of his brother’s followers, Park Eung-ryong, and his associates to the Palace in Hanyang. But the evil creatures are already in the palace, and Kim Ja-joon, the minister of the military, uses the monsters to overthrow the dynasty. Gangrim requests the military to save the people, but the king and the court don't listen to him. When the infected King gets murdered and chaos breaks out in the palace, Gangrim and his comrades close the palace down and fight against all the monsters, especially Kim Ja-joon who has turned into the very creature.