At a high school in South Korea, an incident of child abandonment occurs, and the younger sister, Kijeong, confesses to the crime and is arrested by the police. Learning of this, Yoojeong, who works as a night nurse at a university hospital and is Kijeong's only family, spares no effort to rescue her sister. However, Kijeong remains tight-lipped throughout the investigation, and things only get more complicated. Yoojeong meets Kijeong's close friend Heejin and discovers more about her sister, gradually gaining hope that she can save Kijeong with Heejin's help. However, all of Yoojeong's efforts turn out to be in vain. As Yoojeong finds herself on the brink of giving up everything, she stumbles upon a loophole in the law that could reverse all that has happened and ultimately manages to save her sister Kijeong.