KNOCK KNOCK tells the story of a man who lives with Dissociative Identity Disorder (D.I.D.) - known, until 1994, as Multiple Personality Disorder. It is a rare psychological condition in which two or more distinct identities or personality states are present in an individual and alternately take control of that individual. The person also experiences extensive memory loss. Usually, the primary identity or 'host' carries the individual's given name and is passive, guilty and or depressed.