Life doesn't treat the ordinary Kim family well. They have to live in a damp, dirty semi-basement, steal Wi-Fi from their neighbors, and scrape by on odd jobs. One day, a friend of the Kim family's son, who is going abroad for an internship, offers him a chance to take his place and work as a tutor for a high school girl in the wealthy Pak family. Having forged a university degree, the guy heads to a chic designer mansion and makes a good impression on the mistress of the house. He immediately comes up with an unusual plan to hire his sister.