With her parents and sister dead, her brother abandoning her, Taeyeon cuts herself everynight in rememberance of the pain that was inflicted by her past.

Due to her close-to-insanity state, she is receives a god given power that she is not aware of. She is able to see through people and tell if they were angels or demons. 

Demons and Angels are not allowed to have relationships with humans except their own.

Taeyeon meets Tiffany, a very timid and innocent Angel, who is yet very cold, charming and attractive

Tiffany's main purpose of being there was to help Taeyeon ease back into reality and live a normal life.