DID YOU SAY "ONCE A MONTH"? 
MISSY WIVES STAND NO MORE OF THEIR HUSBAND'S INDIFFERENCE. 
 

Eun-Jai, a career woman, lives with her husband and a daughter.  At a book store, she happens to meet Jin-Woo, whom she thinks she met somewhere before.  A few days later, she comes across him again near her office.  By then she remembers that she met him seven years ago.  The memory of a short moment shared in a train makes them feel attracted to each other, though both of them are married now. 

Eun-Jai's friend, Yun-su, and Jin-Woo's friend, Chang-Se, are also having an affair.  From the beginning, the two couples' relationships are in contrast: Eun-Jai and Jin-Woo' s couple is relatively mild and quiet, while Yun-Su and Chang-Se's couple  focuses on making love, which seems to be a means to forget all kinds of domestic problems. 

By and by, Eun-Jai begins to fall deeper and deeper in love with Jin-Woo, feeling guilty at the same time.  Though Yun-Su and Chang-Se's relationship started through sexual attraction, they are honest with each other in a way.  However, their love affair ends when Chang-Se's wife comes to know about it.  But this gives Yun-Su and Chang-Se an opportunity to start a new life. 

Caught between home and Jin-Woo, Eun-Jai suggests to Jin-Woo that  they make a trip where they met for the first time.