At the kindergarten their sons attend, parents regularly hold social drinking parties known as "Papa-Mama Gatherings." Recently, Karen-chan's mother, a new addition to the school, attends for the first time, introducing herself to the group. Aside from being a single mother, she stands out from the other moms with her model-like beauty, instantly drawing the attention of the fathers. That night, after sending their wives home, the dad friends begin a new relationship with Karen-chan's mother.