During a total solar eclipse, a 25-year-old 21st-century woman, Go Ha-jin (Lee Ji-eun), is transported back in time to the Goryeo Dynasty. She wakes up in the year of 941 in the body of Hae Soo, among the many royal princes of the ruling Wang family during the reign of King Taejo. She initially falls in love with the gentle and warm-hearted 8th Prince Wang Wook (Kang Ha-neul), and later Wang So (Lee Joon-gi), the fearsome 4th Prince who hides his face behind a mask and is given the derogatory label of "wolf dog". As the story develops, Hae Soo finds herself unwittingly caught up in palace politics and the rivalry among the princes as they fight for the throne.
Actor: Lee Joon-gi
Playing as: as 4th Prince Wang So
Actress: Lee Ji-eun
Playing as: Go Ha-jin / Hae Soo
Actor: Kang Ha-neul
Playing as: 8th Prince Wang Wook
Byun Baek-hyun as 10th Prince Wang EunNam Joo-hyuk as 13th Prince Baek-ah
Ji Soo as 14th Prince Wang Jung
Jo Min-ki as King Taejo Wang Geon
Founder of the Goryeo dynasty
Park Ji-young as Queen Yoo (Taejo's 3rd Queen)
Mother of 3rd Prince Wang Yo, 4th Prince Wang So, and 14th Prince Wang Jung.
Jung Kyung-soon as Queen Hwangbo (Taejo's 4th Queen)
Mother of 8th Prince Wang Wook and Princess Hwangbo Yeon-hwa. She was accused of killing Court Lady Oh's fetus.
Kang Han-na as Princess Hwangbo Yeon-hwa (Queen Daemok)
8th Prince Wang Wook's younger sister and 4th Prince Wang So's future consort.
Park Si-eun as Lady Hae Myung-hee
8th Prince Wang Wook's wife and Hae Soo's sixth cousin.
Jin Ki-joo as Chae-ryung
Hae Soo's servant and friend who loves 9th Prince Wang Won. She poisoned Crown prince for 9th Prince.
Seohyun as Woo-hee
A gisaeng who is the last Princess of Later Baekje and 13th Prince Baek-ah's lover.
Z.Hera as Park Soon-deok
Park Soo-kyung's daughter and 10th Prince Wang Eun's wife
Kim Sung-kyun as Choi Ji-mong
The king's astronomer. Crown Prince Wang Mu's best friend.
Sung Dong-il as General Park Soo-kyung
Soon-duk's father and 4th Prince Wang So's right-hand man.
Woo Hee-jin as Court Lady Oh Soo-yeon
Head of the Damiwon Palace, King Taejo's lover, and Hae Soo's mentor who is a mother-like figure to her.
Choi Byung-mo as Park Young-gyu
3rd Prince Wang Yo's father-in-law and the foreign minister.
Park Jung-hak as Wang Sik-ryeom, the king's cousin
Kim Kang-il as a member of the Shinju Kang family