Hi Knightrider,
This sounds like a man in conflict with himself and asks the question: to what length would a man go to stop himself from ?being a mass murderer. Could get pretty ugly! So far so good.
I don't know if DiD is easily, quickly understood. I had to look it up, but that may be me. Even if you spell out the name for the whole thing, there's the issue of people not being up on the new name (no longer Multiple Personality Disorder). But again, that's me.
More importantly, what is the actual trigger that gets the one personality to suspect the other? ?Does he know he has two personalities, or more?
So something along this line is an event that kicks him into .... some action
When a man who knows he has an alternate personality discovers a ?dead body under his bed, he ...
but what is the action?
"takeout ghosts he sees controlling reality"...
that gets a bit fuzzy...
he's going to fight these ghosts, somehow, and this will do what? Put him at peace with his alternate self? Stop the alternate self from killing?
A minor note: "who's" should be "whose"
Good luck with the dramatic logline.
Cheers, SouthWestSusie :)