After four years of marriage, Kana and Masato are starting to see each other's hidden sides. Their arguments over trivial matters have been increasing lately... One day, they reunite with their high school classmate Tsubasa at their reunion. Back then, she was plain looking but has since transformed into a stunning beauty. Soon after, both Kana and Masato are invited by Tsubasa's husband to her house. There, they discover that the secret behind Tsubasa and her husband's happy marriage is swinging - exchanging partners with other couples.

結婚四年目のかなと雅人。お互いの見えなかった部分が見え始め、些細な事で口喧嘩が増えるばかり…。そんな折、同窓会で再会した●校時代の同級生・つばさの家に招かれたかな。学生時代、地味だったつばさは見違えるほど綺麗になっていて…ほどなくして夫婦揃ってつばさの家に招かれたかなと雅人は、つばさ夫婦の夫婦円満の秘訣が夫婦交換だと聞き…