Tae-mu (Lee Tae-sung), after killing his lost cousin in the United States, returns to Korea, claiming that his cousin, Tae-yong (Park Yoochun), could not be found in New York City. Meanwhile, Tae-mu has been having a secret affair with Se-na (Jeong Yu-mi), his secretary, who, in turn, runs into her long-lost stepsister Park-ha (Han Ji-min). Park-ha has been missing for a prolonged period of time and it is revealed that she was in the US after Se-na abandoned her in a truck driving away when she was nine.
Two years after Tae-yong's disappearance, four men dressed in Joseon era garments, fall onto Park-ha's rooftop house. Hungry, homeless and having nowhere to go, the four men decide to stick with Park-ha. Their leader, Lee-gak claims to be the Crown Prince of Joseon (Park Yoochun), along with his entourage - scholar Song Man-bo (Lee Min-ho), personal bodyguard Woo Yong-sool (Jung Suk-won), and palace eunuch Do Chi-san (Choi Woo-shik). One day, Crown Prince Lee Gak sees Se-na who is the spitting image of his beloved wife, who was found drowned in the 18th century. He is convinced she is his wife's reincarnation. Meanwhile, company president Yeo (Ban Hyo-jung) mistakes Lee Gak for her grandson, Yong Tae-yong, because of their exact same appearance, and believes that her long lost grandson has finally returned. Lee Gak realizes that he has time traveled 300 years to 2012, Seoul, to search for the truth behind the mysterious death of the late Crown Princess. In order to approach Se-na, who is also President Yeo's personal assistant, Lee Gak pretends that he is Tae-yong. Tae-mu, believing that he already killed his cousin in New York, lives in constant fear of his devious act being discovered by the family and "Tae-yong" (aka Lee Gak) who claims not to have remembered the event. Tae-mu has always been jealous of Tae-yong's favored position in the family.
On the other hand, Park-ha is shocked by the news that her new friend who calls himself the Crown Prince is, in fact, the grandson of the CEO. But before long, her feelings for Lee Gak blossom and she is hurt when she finds out that Lee Gak, who still holds very tender memories of his dead wife, is courting Se-na. Lee Gak also believes that marrying Se-na in Seoul in the year 2012 would bring him closer to solving the mystery of the Crown Princess' murder in the Joseon era.