To find out the truth about her twin sister Lin Fei in dorm 402, extremely rational "evidence tracking controller" Lin Nan transfers departments and moves in. Facing "fake socialite" roommate Bai Jiani's theft and disposal of stolen goods, public opinion rumors, and crazy framing, Lin Nan step by step exposes her fake facade with everyday hardcore physical evidence. After going through dormitory plotting and jointly counter-attacking external forces, all the way to a public showdown in the thousand-seat auditorium, Lin Nan brings the villains to justice with a rigorous chain of evidence, thoroughly seeking justice for her sister.