Yeong-jae (Sin Joo-ah), Ha-eun (Koo Ji-sung) and Chun-hee (Yoon Chae-i) have been friends for 15 years since high school. Yeon-jae is the youngest of a fine hotel owner and she aims to sleep with 1203 men throughout her life. On the other hand, Chun-hee is an old-school minded high school teacher who has never had sex before in her thirty-something life. Wedding planner Ha-eun was in love with one man for 10 years but recently experienced the pain of losing both her man and work. Then one day, to celebrate their 10th year majority, they have a party of their own in room 1203 of Yeon-jae's hotel. They say the house breaks down if three girls get together.

Seon-mi hands a name card to Joo-hee who is about to get married, saying that she'll be able to feel sexual satisfaction like never before. Joo-hee experiences something new and starts expressing her rising emotions to her fiance despite the time and place. Unlike Joo-hee who is enjoying this, Min-woo is getting tired. He tries to satisfy her to the best of his abilities and even asks for advice from friends but it's not enough. What is that place that has her upside down like this?

A jaded psychiatrist sees a client who is having hallucinations. He uses hypnotism to seek answers into her dark past, but soon gets wrapped up in her delusions and starts to fall for her charms...