The 4th Season of EXO's Travel the World on a Ladder is back with more powerful stories. Ready to laugh! Great chemistry! When they're together, their sense of humor gets better! From incredible ladders to mysterious missions, their special trip of ladder begins in the coastal cities, Geoje&Tongyeong.

During a total solar eclipse, Go Ha Jin (IU), a 25-year-old woman from the 21st century, finds herself transported back to the Goryeo Dynasty where she awakens in the body of Hae Su, a 16-year-old girl. There, she finds herself entangled with ruling Wang family and the princes' rivalries as they fight for the throne. Hae Su develops feelings for the eighth prince Wang Uk (Kang Ha Neul), whose gentle countenance hides his deep ambitions and willingness to make ruthless choices. She also builds a relationship with the feared fourth prince Wang So (Lee Joon Gi), whose cruel and aloof reputation precedes him. However, Hae Su soon recognizes that his coldness is just a front to hide his pain, and helps bring out his true self, falling for him in the process. Will Hae Su's love end up changing history? This drama was adapted from the 2005 Chinese novel of the same name by Tong Hua.