The hilarious thriller Diary of a Psychotic focuses on the killer's lost diary. The protagonist Lu Dongzhi is weak and kind. After attempting suicide on the roof of an abandoned building, she accidentally witnessed the scene of the murder, found the murderer's diary, and ran away in a hurry, but was knocked down by a policewoman, Shen Baojing, and lost her memory. After amnesia, Lu Dongzhi, who happened to read and write this encrypted diary, mistakenly thought he was the murderer and began to imitate "the former self".