Morton Prince was an American physician and psychologist; his book "Dissociation of a Personality" was the best-seller at that time. It tells the story of Miss Christine Beauchamp, who was suffering from MPD (Multiple Personality Disorder). Miss Beauchamp have several personalities, namely B1, B2 and B3. There was a hidden memory in these three personalities. Miss Beauchamp was B2. B2 knows about B1, B3 knows both B1 & B2, but B1 knows nothing about B2 or B3. The strongest personality accounts for most of the time, and it will take over the others and become the main personality at the end. This case and theory give great help to crime investigation. The Beetle, featuring menacing foreign mesmerists, hypnotising villains, somnambulistic criminals and spectacular dissociations of personality. Such figures and tropes were not merely the stuff of Gothic fiction, however; from 1875 to the close of the century, cases of dual or multiple personality were reported with increasing frequency.