Mila Grey lives in apartment 5A. Her parents were shot to death in an alley when she was fifteen. She spends her days reading, and desperately searching for her parents killer. Harry Styles lives in apartment 5B. He is a well skilled assassin who fled from his family at the age of sixteen, because he quickly understood that everyone he loves will be used against him. What happens when she finds her ghost of a neighbor bleeding half to death outside her door? And will he ever open up to her, or forever remain a locked door without a key?