A rather clever premise, somewhat foreboding, and two or three major twists and turns, but ultimately unbelievable, and believability is key.
Like many slow-burn B-movie thrillers (the sort that only work if characters never communicate openly with one another), Don't Tell a Soul requires such huge suspensions of disbelief and outright implausibility that it never really grabs you by the shirt collar to not let go.
Instead, you're left watching and constantly thinking, "Oh, yeah, that'd never happen like that."
Second only to boringness, implausibility is a fatal movie flaw in my book.
