Xiao Yu, a middle school student, lives with his widowed father, a mediocre detective who runs an unprosperous detective agency. Every day, his father trains Xiao Yu professionally hoping that he could be a great detective in future. One day, when Xiao Yu stalks a suspicion gang, he barges into a criminal scene, and gets framed by the real murderer, but with his super memory, shrewd observation and sharp deduction, and the help of a mysterious girl, he successfully clears the suspicion cast on him...