With her husband transferred to a regional post, mother Yuka lives with her children and son-in-law Takeshi. Tormented by the loneliness of being apart from her husband and aware that her daughter's marital sex life has dried up, one night Yuka accidentally discovers Takeshi masturbating alone. She becomes instantly captivated by his huge cock. Convincing herself it's her duty to relieve her son-in-law's sexual frustration in her daughter's place, she begins seducing him. From that moment on, Yuka constantly craves Takeshi, and their forbidden relationship grows deeper each day.