Yumi suffers from a sexless marriage and secretly begins a relationship with a man she met at a drinking party. However, her son-in-law discovers her affair after secretly watching her, and uses it to blackmail her into having sex. Obsessed with Yumi's huge tits, her son-in-law has long desired her and seizes the opportunity. Though initially reluctant, Yumi gradually becomes accustomed to being touched and fondled by him, even while remaining cautious of her family. Eventually, she begins to realize she is actually enjoying the forbidden relationship.