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.

While under heavily armed guard, the dangerous convicts aboard a cargo ship unite in a coordinated escape attempt that soon escalates into a bloody, all-out riot. But as the fugitives continue their brutal campaign of terror, they soon discover that not even the most vicious among them is safe from the horror they unknowingly unleashed from the darkness below deck.

The drama is about a first-class impersonator of a trot singer named Lilac, and his daughter Shin-hye in the process of getting away from the deceptive acting and finding real happiness.