Over the years, Kevin has been treated by his psychiatrist Dr. Karen Fletcher, and appears stable: within his mind, all of his personalities sit in chairs in a room, waiting for their turn "in the light", i.e. controlling the body, while "Barry" controls who gets to go in the light.
"Dennis" masquerades as "Barry" and attends a meeting with Fletcher, but she realizes that "Dennis" and "Patricia" have supplanted "Barry" as the dominant personality.