After losing her husband in an accident, Satomi lived with her daughter, but two months ago she started living with her married daughter and son-in-law. She was happy about this, but whenever she heard the sounds of her daughter and son-in-law having sex at night, her body would heat up. However, there was no one else to satisfy her desires, so she continued to satisfy herself by masturbating. One day, on her way home from shopping, Satomi had the urge to pee and wet herself in the entranceway. Seeing this, her son-in-law got an erection. "It's all your fault, mother-in-law..."