Kang Jae-hee's double life begins. She's Yoon Yi-jun's secretary by day and a detective by night. Yi-jun keeps testing her, but Jae-hee relentlessly keeps an eye on him and searches for the missing phone. She plans to infiltrate the room that's banned from entering, but Yi-jun doesn't let his guard down easily. Their relationship takes a strange turn through unexpected physical contact.

Yi-jun stays prickly but starts trusting Jae-hee. Jae-hee notices something suspicious about the milk Yi-jun was drinking and realizes he is being threatened. The investigating team thinks the perpetrator could be someone else. Jae-hee finally gets the chance to enter the room that's been banned from entering. She searches for the missing phone in the room but immediately faces danger.

The investigating team finds traces of herbicide in the milk and suspects that someone is after Yi-jun. Jae-hee keeps an eye on Yoon Na-jung, the ambitious second daughter of Taekang, and follows Yi-jun to the family dinner, which is full of tension. Chairman Yoon makes an unexpected decision, causing a stir. Jae-hee joins Yi-jun for a drink and her drinking habit starts coming out.