She sits under the tree and gazes at the yellow dazzing moon that adorns the sky. To her, the Moon resembles the happiness she longs for with someone she loves. She cherishes him and appreciates his presence. The Moonlight resembles the unconditional love he showers her. Her entire heart soaks in the gentleness, sending love signals all around her body, every time she spends time with him. She can't do without him; she can't imagine that happening.

Her nightmare turns out to be the reality. The black clouds emerge and conceal the moon out of her sight. She can't catch a glimpse of the moonlight; all she see is only The Moon's Shadow. She is lost in the world of darkness where her happiness is stolen. The hopes and desires she embraces vanish in a mere second...

Fate pulls Kim Taeyeon and Kris Wu together as they pursue their studies in the Seoul Arts High School. They falls in love with each other and plans to further their studies abroad after graduating from their high school. However, things doesn't go as what they has planned. Kris' cousin, Park Jiyeon, has been harboring an requitted love for him and approaches a man, Byun Baekhyun, who knows magic, to cast a spell on Taeyeon. She is then stricken with a dread disease and suffers from throwing out blood frequently. Not wanting to burden Kris, she chooses to leave silently.

Baekhyun falls in love with Taeyeon before knowing that she is the girl Jiyeon has previously asked to cast a spell on. Turning his back on Jiyeon, he gives Taeyeon a bottle of potion to drink so that she will able to recover after being in a deathlike coma for 3 days and nights. Soon after, Kris learns about her illness but finds her on the death bed. Assuming she is dead, he marries Jiyeon and is handed over her parents' cosmetic company even though he has never loved her.

After 3 days and nights of deathlike coma, Taeyeon wakes up from her unconsciousness but has lost her memories. She has taken Baekhyun for her boyfriend and follows him to America to further their studies. After 5 years, they returns to Seoul.

And they meet. Will the moon unfold itself again? Or is it just The Moon's Shadow?