Nerariyan CBI (transl. To know the truth CBI) is a 2005 Indian Malayalam-language mystery film directed and produced by K. Madhu and written by S. N. Swamy. The fourth installment in the franchise of CBI investigative thrillers, Mammootty reprised the role of Sethurama Iyer, a Central Bureau of Investigation officer, with Mukesh and Jagathy Sreekumar reprising their roles as the associate officers Chacko and Vikram respectively and the background score composed by Shyam.Like its prequels, Oru CBI Diary Kurippu (1988), Jagratha (1989) and Sethurama Iyer CBI (2004), Nerariyan CBI was also set as a murder mystery behind a lady, who found dead at a haunted mansion in suspicious condition.