Oh Sung Moo, the father of cardiothoracic surgeon Oh Yeon Joo, mysteriously goes missing while writing the last chapter of his webtoon "W". Yeon Joo goes to his office looking, but a hand from his monitor suddenly pulls her in, and she finds herself on the rooftop of a building, next to a bloodied man. She manages to save the person, only to realize that he is Kang Cheol, the main character of her father's webtoon. Yeon Joo later discovers she can only enter and leave the webtoon depending on Kang Cheol's feelings.