Considering the age of the Samurai, the doctor's time and timeless love and truly modern King created by the process of Green TV
After King Gongmin of Goryeo marries the Yuan princess Noguk, they return to Goryeo.
On the way they are attacked and the queen is fatally injured.
According to the advice of his soothsayers, the king orders royal bodyguard Choi Young to pass through a mystical portal ("heaven's gate") and find "heaven's doctor."
Choi Young travels to the future and brings back Yoo Eun-soo, a modern-day doctor from Seoul, who saves the queen's life.
He makes a promise that he will return her to her world, but the kind-hearted yet powerless King Gongmin forces Eun-soo to stay as she can be useful to him.
As Eun-soo accustoms herself to her new surroundings, gradually she and Choi Young fall in love with each other.
But problems arise as others become fascinated with her strangeness and apparent ability to predict the future, and Eun-soo becomes a pawn in the political power plays between Gongmin, the Yuan overlords, and the sociopathic nobleman Ki Chul.
Constantly risking his life, Choi Young thwarts numerous attempts by Ki Chul to kidnap and possess Eun-soo, the worst of which almost results in the death of the king and queen.
Choi Young selflessly brings Eun-soo to the portal before it closes, but before Eun-soo can tell him that she's decided to stay, Ki Chul's soldiers attack them and Choi Young suffers a life-threatening wound.
Eun-soo enters the portal, hoping to save him by gathering medical supplies from the future.
But when she passes through, she finds herself in the era a hundred years before Choi Young's time.
There, she spends a lonely time for the portal to open again, while leaving hints for her future self.
One day, "heaven's gate" opens again and Eun-soo enters, only to find herself again back in modern-day Seoul. But she finds life empty without Choi Young, and she re-enters the portal.
Eun-soo reaches the time period five years after she left him, a time during which Choi Young had brilliantly won a number of military campaigns.
Finally she and Choi Young find each other again.