The first sequence of stills depicts a group of incoming police university students enjoying their summer vacation together. After a tumultuous semester, Kang Seon Ho (Jinyoung), Oh Kang Hee (Krystal), No Beom Tae (Lee Dal), and Jo Jun Wook (Yoo Young Jae) go to the beach.
Oh Kang Hee, who had figured out the truth behind the mysterious connection between the police university and the illegal gambling case in previous episodes, formed an investigating team alongside No Beom Tae and Jo Jun Wook to assist Kang Seon Ho. Oh Kang Hee's mother, Oh Jeong Ja (Kim Young Sun), provided important information, while Professor Kwon Hyuk Pil (Lee Jong Hyuk) assisted the others in their inquiry. Kang Seon Ho and Yoo Dong Man (Cha Tae Hyun) were able to race to the location and arrest the suspect Go Deok Bae thanks to their assistance (Shin Seung Hwan).
After all of this, the young investigating team is taking a break, taking selfies and acting silly for the camera, and ditching their uniforms in favour of casual attire. During the friends' vacation, Kang Seon Ho and Oh Kang Hee use the opportunity to exchange meaningful stares, as if on a date, leaving No Beom Tae and Jo Jun Wook to stare after them. On the professor side, the atmosphere was less welcoming, since KBS also revealed stills of Cha Tae Hyun and Hong Soo Hyun as Yoo Dong Man and Choi Hee Soo, respectively.
Choi Hee Soo, who made viewers suspicious with her phone call to someone saying, "We have to stop things before then," right before Go Deok Bae was detained, seems worried and taken aback when confronted by Yoo Dong Man. What is her secret, and will Yoo Dong Man be able to bring his inquiry to a victorious conclusion?