The drama is adapted from the novel by "Queen of Reasoning" Agatha Christie, and tells the story of a mother's process of clarifying her guilt and finding out the truth. Kim Yun-jin plays the heroine Ms. Ma in the drama, who is falsely accused of killing her daughter. Jung Woong-in plays the detective Han Tae-gyu in the drama. He was in charge of the Ms. Ma incident when he was a rookie. Now he is a single detective in his 40s. After Ms. Ma escaped from the treatment and guardianship center, he stubbornly tracked her whereabouts. Because of his stubborn persistence, for Ms. Ma, he is like the police chief Javert in "Les Miserables". With the help of younger detectives, he tracks down Ms. Ma's whereabouts.