- Subtitles: English
After King Gongmin of Goryeo (Ryu Deok-hwan) marries the Yuan princess, Noguk (Park Se-young), they return to Goryeo. On their way, they are attacked, and the queen is fatally injured. According to the advice of his royal advisor, the king orders the Captain of the Royal Guard, Choi Young (Lee Min-ho), to pass through a mystical portal ("heaven's gate") and find the "heaven's doctor". Choi Young travels to the future and brings back Yoo Eun-soo (Kim Hee-sun), a modern-day doctor from Seoul, to save the queen's life. He promises that he will return her to her world once she saves the queen, but the royal advisor schemes and persuades King Gongmin to force Eun-soo to stay as she can be useful to him.
As Eun-soo accustoms herself to her new surroundings, she and Choi Young gradually fall in love with each other. But problems arise as others become fascinated with her as the "Heaven's doctor", and Eun-soo becomes a pawn in the political power plays between King Gongmin, the Yuan overlords, the sociopathic nobleman Ki-Chul (Yu Oh-seong) and Prince Deok-Seung (Park Yoon-jae), King Gongmin's uncle. Constantly risking his life, Choi Young thwarts numerous attempts by Ki-Chul and Deok-Seung, who are out to have Eun-soo in their possession.
The series follows how Choi Young and Eun-soo evade and overcome impending problems and whether or not they succeed in getting her to heaven's door in time before it closes for good.