Agree with Trix.

Should it read “mysterious cult OF his own personalities”?

So one of his personalities is being held captive in his mind – I kinda like this idea. Similar(ish) premise to Identity. Goal of escaping is good, makes sense BUT since all of this is happening inside the character’s mind, I want to know what this represents in the real world. If he escapes, does that mean his true personality carries on existing in the real world? If he perishes, what does that mean in the real world? There are no stakes yet. I need to understand that to understand why I care, especially when you’ve made it clear that this is all in a character’s head.

The girl… what does she represent? She’s another personality? Given that we know he’s being held captive by his own personalities, surely saying “may or may not exist” is redundant. She can’t exist because it’s all happening inside this guy’s head.

My suggestion, make it so the main personality is free but discovers a girl is being held captive and he then must go and rescue her putting himself at risk. Give us a reason why. It’s his sister or something. And, as Trix suggested, don’t tell us this is all in his head. That’s the twist and wouldn’t happen until the end of Act II probably.

Whilst the twist might be the most interesting part, a logline for The Empire Strikes Back would NEVER reveal that Vader was Luke’s father. One for 6th Sense would NEVER reveal that Bruce Willis was dead all along. I could go on. The twist and the hook are completely separate. If you think it’s a little boring without that, try and spice it up so the twist is still a secret.