Jisook works as an instructor at Smile Club, a laughter therapy program at an insurance company. She stresses the importance of laughter, and seems cheerful all the time. Yet, in reality, she finds life tough and exhausting. Then one day, life gets even more complicated when her son Jaeho uses violence against his classmate Donghyun – who happens to be the son of Heesoo, the leader of Smile Club. Since Heesoo is an important client, the incident puts Jisook in a rather difficult position.