A girl wakes up in a huge secret laboratory, then accidentally meets another girl who is trying to protect her house from a gang. The mystery girl overthrows the gang with her unexpected powers, and laboratory staff set out to find her.
An assassin named Tae-goo is offered a chance to switch sides with his rival Bukseong gang, headed by Chairman Doh. Tae-goo rejects the offer that results in the murder of his sister and niece. In revenge, Tae-goo brutally kills Chairman Doh and his men and flees to Jeju Island where he meets Jae-yeon, a terminally ill woman. Though, the henchman of the Bukseong gang, Executive Ma is mercilessly hunting Tae-goo to take revenge.
Ancient Korea, 1506. The tyrannical King Yeonsan-gun of Joseon is overthrown by his half-brother Jung-jong, whose reign begins with a blood bath. Over the years, traitors plot against him, sinking the kingdom into chaos. In 1528, frightened rumors come to royal palace, regarding a mysterious creature, known as Monstrum by the peasants.
