one, yes, he spent the entire movie, deadpan narrating. just going through the motions. Losing Grace destroyed him. she was his only friend, and probably liked her. the genius kid detective couldn't find his kidnapped best friend. the cops didn't include him in the case at all. he wasn't a failure as an adult because he was a shit detective or anything. he was a failure because losing Grace broke him. Confidence, ambition, etc. totally shut down. His life falls apart, as he just coasts along on past exploits.. never moving on.
so yeah, he finds out the principle he respected, kidnapped her, and had her in his shed for 20 years.. and the girl he befriended for the new case was her daughter.. Graces mind is totally broken.. and he just keeps up the deadpan narration. Until the end. where he finally lets himself feel again, and totally breaks down. cut to title and credits.
mike and jay called the cut/ending comedic. I'm not sure on that.. I felt it was more heartlifting. His life was stunted by the kidnapping. this was him coming to terms with it finally, so he can start living again.