Eun Ha-Won is a college student. She is a bright girl who wants to be a veterinarian, but at home she is lonely. She is isolated from her family members. Eun Ha-Won lives with father, step-mother and step-sister after her mother died in a car accident. One day, she helps a mysterious old man. The old man suggests to her to live in a mansion and pursue her dream of becoming a veterinarian. Since than, she moves into the mansion and lives with three cousins Kang Ji-Woon, Kang Hyun-Min, Kang Seo-Woo and their bodyguard Lee Yoon-Sung.

A man named Shin Woo regrets letting his first love go ten years ago because he didn't have the courage to confess. However, he gets the chance to win her again when he travels back in time, and this time he's armed with the knowledge that she liked him back then too. Unfortunately, he has a pretty strong competitor: himself from ten years ago. The present Shin Woo and the past Shin-woo engage in a fierce rivalry to win their love's heart.