Minho is the only child of a librarian. His mother owns a library right on top of their apartment. One rainy day, a girl came to their doorsteps soaked with water from head to toe. She claimed she can't remember anything except her name, Krystal.

Minho's mother took her in. Mostly because she always wanted a daughter and the girl in front of her is very pretty and polite. They treat her like their own flesh and blood. Except for Minho. He hates her guts. He thinks Krystal is hogging all the attention from his parents. And also the fact he has to sacrifice his room for her.

Who is this 'Krystal'?

Whatever will happen to these two?