Mangled body parts have been turning up all over Seoul and the inhabitants are scared. Ten murders in ten weeks, all committed with a pocket knife, and still, nobody has a clue who the creepy killer is.

Kim Jong-in is a handsome and charming detective with a fondness for blood. He doesn't know it yet, but he's is the only one who can stop the wild killer.

When her brother, Park Chanyeol, is kidnapped, just graduated High School student Ha Na Yeong finds herself thrown into the center of the investigation. Her only clue is a bloody record she found in her brother's shattered apartment.

She enlists the help of Kim Jong-in.

Can Ha Na Yeong help Kim Jong- In overcome his blood addiction and find the answers before the arrogant killer and his deadly knife strike again?