After his girlfriend died in a car crash, sorrowful psychologist Chung Tai Yin spends five years investigating the truth of the incident. His girlfriend once conducted a psychological assessment for a schoolyard murderer. Her report indicated that he lacked a motive or violent tenancies. During the course of his investigation, Chung Tai Yin meets Tung Yat, a genius with Asperger syndrome, and his sister Tung Yuet, whom he is mutually dependent with. Tung Yat's lack of social skills gives Tung Yuet a lot of trouble. Many years ago, it even caused police officer Wu Tin Yeung's undercover mission to fail. But because of Chung Tai Yin, they eventually become friends and help Chung Tai Yin with finding the true killer. Wong Hoi Ching, a witness in the case who could not be contacted for many years, suddenly appears and visits the murderer in prison, causing drastic changes in the case.