渡边美都（波瑠饰）与“第二喜欢的人”凉太（东出昌大饰）结婚后，在偶然的机会中遇到了初中开始一直爱恋的同班同学有岛光轨（铃木伸之饰）。虽然二人都已成家，但是美都却发觉自己回忆起了恋爱的感觉，于是开始了婚外情。美都对外遇没什么罪恶感，她只考虑自己的感受，甚至后悔选择结婚，把一切归咎于命运。美都的丈夫凉太、光轨的妻子丽华（仲里依纱饰）都怀疑自己的伴侣出轨，从此两个家庭陷入了混乱的四角关系

Mitsu is a 29-year-old woman who married “the number 2 man in her life,” but has been unable to forget her first love, Arishima. When she accidentally encounters him after several years, she feels that it is destiny, and the two spend one night together in secret without their spouses knowing. Arishima himself has just begun a family of his own, with a newborn child, but he and Mitsu find themselves continuing their affair. While at first they enjoy what seems to be a no-strings-attached affair, it gradually begets subtle changes in feeling. Mitsu’s husband, Ryota, becomes aware of the affair and ups his devotion to her in an attempt to keep her by his side. Arishima’s wife, Reika, a perfect mother and devoted wife, makes this four-way relationship an increasingly complicated web of mixed emotions.

二組の夫婦のマリッジライフと四者四様に揺れる恋愛模様を、予測不能な展開で繰り広げていく本作。“2番目に好きな人”と結婚した主人公・渡辺 美都わたなべ みつが、ずっと想い続けていた中学時代の同級生と偶然再会したことからすべてが始まる──。恋の始まりはいつだって予想もつかず止められない。それはたとえ結婚後でも。昔はぐれた運命の人が突如目の前に現れて、ずっと封印していた恋が目覚めてしまったら──。その気持ちを押し殺すことはできますか？

運命だと信じていた男との再会に心を揺さぶられる女。

不倫されたと知っても妻を愛し、責めない男。

浮気をしている夫を手のひらで転がす妻。

軽い遊びのつもりが抜けられなくなる男。

それぞれがそれぞれのやり方で大切なものを守ろうとする姿に、人間の狡さや弱さが描かれる大人のいびつなラブストーリー。

안과에서 일하는 미츠는 첫사랑을 묻어둔 채 료타와 결혼하게 된다. 그러던 어느 날, 학창시절 첫사랑이었던 아리시마와 우연히 만나면서 단조로웠던 미츠의 일상이 흔들리기 시작한다.