From Now On, Showtime!: 1x8

The Enemy Within

Head Yoon lies unconscious at the hospital, and it turns out that the culprit is none other than her closest partner. Realizing that she has made the wrong call, Seul Hae starts the investigation from the beginning, focusing on the right suspect. The investigation continues, and Seul Hae and Cha Woong come up with a little magic show that would lead the suspect into confessing the hard evidence.