Eriko, driven by her husband's lack of sexual interest, has poured all her affection into her only son, Shinkichi. As Shinkichi matures, he gradually begins to desire his mother's body. One day, her brother-in-law Toshio visits the house. Learning about her troubled marriage, Toshio becomes intrigued by Eriko and starts fondling her. Caught in the act, Shinkichi witnesses his mother's lewd behavior, shocked yet instantly aroused as his cock grows harder and hotter than ever before.