My wife doesn't know... A lewd signal for my stepmother and me

Mari lost her husband and lives with her daughter Yuko and her son-in-law Kyo. Yuko often does not travel as a hobby, and Mari often spends time with Kyo. One day, the two end up having a twisted relationship due to a random event. Despite being tormented by guilt towards Yuko, the two are unable to contain their lustful bodies, and promise to "seek each other on the night when Mari wears perfume." And today, again, in front of Yuko, who is not sure what they would know about their promises, the lustful Mari wears perfume...