How to teach a lesson to a guy having an affair

Overview

Due to her past, Na Na is hypersensitive about cheaters. After witnessing an affair, she posts on a website what the two, who work at Revan company, did at the bar. However, she hasn't decided whether or not she'll tell Roo Mi what she saw. Roo Mi suspects that there's something going on between Gyu Min and Jang Mi.