Mu Xia is a talented locksmith. While dealing with a strange murder case within a locked room, Qin Zuo Man inadvertently discovers that Mu Xia is the new security consultant hired by the police academy. As more locked room cases arise, the simple-minded Qin Zuo Man, the monotonous Mu Xia and celebrity cop Tan You join hands to form an investigative team that seeks to uncover the truth through every door.