Happiness battle of people who don't need to be happier. There are four mothers who live in the most expensive apartment in Korea, send their children to the best school, and have hundreds of thousands of followers on social media. Even though they are already happy enough, one of them (Eugene) is found dead in the midst of fierce competition on social media to see who is happier. Miho, a bank clerk who was the sister of her dead Eugene, hears the news and takes on her nieces and nephews who are not of her blood. Afterward she enters the moms' community of them. While tracking Eugene's death through SNS, she encounters the bare face of a happy family and the cruel truth of the past...