This is a time-travel, historical, romantic-comedy drama featuring the unique story of Crown Prince Lee Gak, who is transported 300 years into the future to present day Seoul along with his three retainers. Their duty to solve the murder case of the Crown Princess in order to return to Joseon. They land in the rooftop apartment of Park Ha, a cheerful woman in her mid-20s, who eventually believes the odd quartet’s predicament and becomes their guardian. As Park Ha educates the four on life in the 21st century, Lee Gak comes across Hong Se Na, who seems to be the reincarnation of his wife. Taking on the identity of Yong Tae Yong, Lee Gak slowly begins to unravel the murder of Yong Tae Yong and in turn moves closer to solving the murder case of the Crown Princess. As he finds himself in love with Park Ha, he figures that maybe the mystery of Crown Princess is not as what he had expected.
- Micky Yoochun (Park Yoochun) as Lee Gak / Yong Tae Yong
- Choi Won Hong as young Lee Gak
- Han Ji Min as Park Ha / Bu Yong
- Jun Min Seo as young Park Ha / young Bu Yong
- Lee Tae Sung as Yong Tae Moo
- Jung Yoo Mi as Hong Se Na / Hwa Yong
- Kim So Hyun as young Se Na / young Hwa Yong