Kim Soo Hyun always pushed her daughter, Saet Byeol, to not only do well in school but also to always come in first place. But tragedy strikes when Saet Byeol is kidnapped and killed, leaving Soo Hyun and her husband, Han Ji Hoon, with no clues as to who could have done such a terrible thing and why. Detective Ki Dong Chan struggles to find the killer, while Hyeon Woo Jin, who shares a past with Soo Hyun, tries to do what he can. But Soo Hyun is given a chance to go back in time to change the course of events.