O Yeon Ju, a cardiothoracic surgeon, is thrown into a surreal mystery when her father—creator of the popular webtoon "W"—suddenly disappears while working on its final chapter. While searching his office, Yeon Ju is pulled into his webtoon through the monitor and finds herself beside a wounded man on a rooftop. That man is Kang Cheol, the story’s main character. After saving him, Yeon Ju realizes she can only travel between the real world and the webtoon based on Kang Cheol’s emotions.