The Smile Has Left Your Eyes (Season 1)

A detective thinks about quitting his job. He takes on a female university student murder case that was disguised as a suicide. The detective becomes obsessed with solving the case. He has a young sister and she meets a man. The man does not remember when he was little. He is not a good person, but she has sympathy for him. The detective tries to push the man away from his younger sister. The detective suspects that the man is somehow involved in the female university student murder case. The man and the detective's younger sister fall in love.