Suzuhara Mugi is a 15 year-old on a mission. She is determined to somehow get onto the campus of Shoukei Academy, a super, super elite high school.
The school is huge and private and has tight security.

Mugi is searching for her missing older sister, her only remaining family, and she has been led to believe that someone or something on the campus of that school will help her in her search. Unfortunately the strict school security is preventing her from getting onto the school grounds.

However, her luck changes when she literally runs into Midou Kazuya the son of an insanely rich mega-corporation president, and an elite person at the school. Midou is not impressed with Mugi’s sob story about needing to get into the school. He is a very smug and arrogant rich guy. But he can be reasonable, and he eventually strikes up a deal with Mugi, he will get her onto the school grounds in exchange for some labor on her part, she must come to his house and work as a maid! He lives with 3 other guys, known as the La Princes in the super elite school.

[Edited from Wikipedia]