Woo-jin and Samuel used to be deeply in love and very passionate about each other. However, after being married for a long time, the days of burning with sexual desire are long gone, and they become a sexless couple. One day, Samuel finds out his friend, Jung-soo, is having an affair. Woo-jin insists on telling Se-yeon about the truth.

As life hits them hard, Samuel and Woo-jin decide to work together and blacklist the couples who are cheating on their partners for money. Woo-jin finds targets from the hotel she is working at, and Samuel puts a tail on them. Meanwhile, despite their financial difficulty, they spend the money they made on Samuel’s father’s birthday and Woo-jin’s niece’s academy fee.

Samuel and Woo Jin look for another target. An old man comes to Woo Jin's hotel and it seems like he is having an affair. Samuel and Woo Jin follow the couple to the mountains and the sea to gather evidence that they can use to blackmail the couple. However, the old man suggested that they meet at his company if they both wanted to get money from him.

Woo Jin goes to the hospital and Samuel is not in bed. It turns out that Samuel is with Min Soo, his neighbor and cleaning friend in the past. Woo Jin calls him and catches him lying. He decides to follow him to see what's going on.

Woo Jin thinks about his relationship with Samuel and tries to figure out when and where everything started to go wrong. Feeling betrayed, he decides to blackmail the woman next door. Woo Jin interrogates Samuel, and Samuel tells him the secret he's been keeping. Woo Jin is confused, and that leads to big fight. What will this couple end up like?