Eun Ha-Won is a bright high school senior who dreams of becoming a teacher. Unfortunately, she loses her mother in a tragic accident. When her father remarries and a cruel stepmother moves in and steals Ha-Won’s college tuition, Ha-Won is forced to take on part-time jobs to make her college downpayment. One day, she meets an old man who convinces her to move into a gorgeous mansion with three equally gorgeous men, who also happen to be billionaire cousins and heirs to the Kang family fortune. Between the rebel-minded loner Kang Ji-Woon, playboy money machine Kang Hyun-Min and the super-sweet singer Kang Seo-Woo, Ha-Won finds herself in the middle of the hottest love quadrangle to ever befall a modern fairy tale princess. Rounding out the mansion's chaebol lifestyle are Lee Yoon-Sung, who serves as the cousins’ handsome bodyguard, and Park Hye-Ji, a gorgeous girl, who's been neighbors/in love with Hyun-Min since childhood.
Shin Dong-mi as Han Jung-sun – She died before the main events of the show. Eun Ha-won's father believed her to be unfaithful to him, but this was proven to be false. She died alongside Kang Ji-woon's mother, trying to save her. Kang Ji-woon's mother entrusted her with her wedding ring to give to Kang Ji-woon, but this ring ended up being mistakenly given to Eun Ha-won.
Jin Hye-won as Hye-ji's friend
Jung Young-joo as housemaid
Kim Jin-tae
Jo Kyung-hoon as Ji-woon's boss
Kim Kang-hyun as Seo-woo's manager
Lee Ah-hyun as Seo-woo's mother – She is very easy going and somewhat childish, but still loves her son a great deal, and is still very much in love with her deceased husband, Kang Seo-woo's father.
Son Seon-geun
Park Kyu-jeom as Director Kim
Gong Da-im
Park Hyo-jun as customer in car center
Kim Kwang-seop
Jo Eun-suk as Hyun-min's mother – cold and arrogant, she only cares about her son succeeding Haneul Group, constantly pressuring him to stay as the main heir.
Gong Jung-hwan as Kang Young-jin – He was mistaken as Eun Ha-Won's biological father, but this turned out to be false. He tried using this false information to his advantage by getting money from Kang Ji-Woon to pay his debt, but was foiled by Eun Ha-won.
Jin Ju-hyung as Jun-su
Na Jong-chan as Joon Soo - Asks Hye-Ji on a date.
Kim Ji-sung as Ji-woon's mother – Deceased before the events of the show; she dies alongside Eun Ha-won's mother and begged Ha-won's mother to give her ring to Kang Ji-woon as her dying wish. She didn't let Ji-woon's grandfather know him for fear that he would not be able to love someone without the worry of social status and might be ripped apart like her and Ji-woon's father were.
Kim Young-jae as Ji-woon's father – He was forcibly separated from Ji-woon's mother by his own father who believed that people of different social classes should not be together. It is believed he died before he could ever find out about his son.
