Oh Sung Moo, the father of cardiothoracic surgeon Oh Yeon Joo, mysteriously disappears whilst writing the final chapter of his webtoon "W". Yeon Joo goes to his office to look for him, but a hand suddenly pulls her out of her monitor and she finds herself on the roof of a building, next to a bloodied man. She manages to save him and realises that he is Kang Cheol, the protagonist of her father’s webtoon. Yeon Joo then discovers that she can only enter and leave the webtoon depending on Kang Cheol’s feelings.