Bang Myung-soo is a popular writer of webtoons. He then writes a webtoon series about his past relationships, specifically his four ex-girlfriends, which includes an older, wealthy divorcee, a chic and successful woman who works at an investment firm, and a third-rate, airhead actress. The webtoon reveals plenty of details about Myung-soo's love life, and it becomes a huge hit. Soon, Myung-soo is considered a cross between Public Enemy Number One and National Heartthrob, and his webtoon gets adapted into a movie.
Kim Soo-jin is a film producer who's prepared to do whatever it takes to save their failing production company. Because of this, she accepts the assignment to produce a webtoon adaptation. But to her horror, Soo-jin belatedly finds out that the webtoon artist is her ex-boyfriend Myung-soo, and that she's one of the girlfriends he wrote about. And as the movie starts shooting, the project also brings Myung-soo's other ex-girlfriends back into his life all at the same time.