Humanity is under attack by parasitic organisms that seize control of the brain in order to fully dominate the body and devour other people. One of them failed to establish full control over its host and is now forced to coexist with her, manifesting only in moments of mortal danger. While the girl is in horror, trying to come to terms with her new identity, the other parasites have organized themselves and, through joint efforts, are securing food for themselves, and the Korean police have become the first in the world to create a special unit to combat this unprecedented threat.