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.

Hae-gap is a director who makes anti-government documentary films. One day, Hae-gap’s son, Na-ra, runs away from home, but Man-deok, a freeloader living in Hae-gap’s house ends up bringing him back. Later, Man-deok raids the head developer of Deul Island to stop its exploitation, and Na-ra helps and ends up getting caught. In order to bring Na-ra out from jail, Hae-gap signs to stop making anti-government films and moves to Deul Island with his family. Na-ra sees his father leading a good, quiet life there and starts opening up. But when a construction company charges in to clear-out the island and the islanders fall at risk of losing their homes, Hae-gap leads a strike against it and his family fall in grave danger...