Three nights before enlisting, Seung-wook decides to leave his mark since he can't avoid the military so he flirts with everyone. However, his school senior So-yoon nor his blind date Il-hong will fall for him. The night before he leaves for the army, Seung-wook decides he's going to see some action with the two girls. The project of 'leaving a mark' starts now.

Joon-ha had the best night of his life with an older woman he met while drinking. He starts looking for her as he can't forget the feeling and finally they meet. However, she's going to become his new stepmom. She's his father's girlfriend. When the three start living together, things turn edgy and then dangerous when his father leaves the house one day.

Gyeong-soo and Jeong-min used to be the happiest couple in the world. However, Jeong-min is left home alone after her husband leaves to the regional area for a lengthy business trip. While she tries to deal with her lonely feelings, her son’s tutor Min-hyeok starts flirting with her hard. And although Jeong-min knows she shouldn’t, she starts being attracted to Min-hyeok more and more. Meanwhile, Gyeong-soo finds his place in a boarding house in the regional district and starts getting attracted to the owner of the board house, who is a single mother with a young daughter.

In the 1980s, Hyeon-soo, who is from a rich family but causes all sorts of trouble, barely makes it out of junior high and makes it to the next grade where he steps out of the 'Hurricane's' line.

Young Se-hee gets married to middle aged Min-goo, but she's not happy with his 'item' as he's old. While she goes on vacation with her husband, Min-goo's daughter Yoo-jin calls her boyfriend Ji-hoon to the house when her parents are not there and they have sex. Meanwhile, Se-hee comes back home early from the vacation because her husband has to work and runs into a completely naked Ji-hoon.

Ju-seong, Min-gyu and Hee-jin live in a boarding house run by Man-seok. One day, Claire, a blonde, Czech, boarding student comes in. To adjust to her new life in Korea, the boarding men help her but it turns out that she’s liberated. The truth is that the men in the boarding house were all approaching her…

"Trust me tonight" Min-ho is preparing to get a job and is spending some time in his parents' house. However, his parents aren't home and only his young sister-in-law is there. His brother Hyeon-soo had left the house after fighting with his wife. Min-ho can't help but feel attracted towards his young and appealing sister-in-law.

Jong-hwan's friend's daughter Seong-hye moves into his house. She messes up the house and drinks with her friends and even has sex with men in the house. One day, Jong-hwan ends up comforting Seong-hye who broke up with her boyfriend. They spend more time together and become dependent on each other. Afterwards, they fall for each other more than they should...

Are we dating? Even if I slept with her? Is it alright for friends to sleep with each other? Pretending not to know, pretending to know all the flirting going around. The flirting goes on any time and at any place! Today with this one, tomorrow with that one and who knows who the day after...