Spoiler-last shot question-spoiler
JUST WATCHED FOR 1st TIME-----SPOILERS- ok, so the last shot of the ice pick at first made me think she was the killer all along (suspense was incredible in the last 5 min making me think he's gonna die then he's not then again then not, maybe she was the killer-maybe it was Beth) Anyway, I felt shortly after thinking a bit more, maybe it was Beth all along and the ice pick next to bed was actually a prop to heighten their sexual encounter similar to the scarf earlier when she tied Douglas up. She asked if he'd been scared and he said something like that's what made it so good or something.
Then I come to the boards here and apparently I didn't see in the book she was printing the partner would be killed in the elevator which basically says Stone was the killer cause who else would have seen that ending she had just written. I'm confused now. Douglas used the stairs- wasn't that where Beth just came from? That's also where they find a wig the weapon and jacket covered in blood. Wouldn't they have seen each other at some point? I guess she could have gone higher up the stairs, but it didn't appear that way.
Anyway, Douglas should have known then Stone was the killer- why screw her and trust her? My only conclusion is that Beth and Stone's character were working together all along playing games like psychologists play. Things however started to unravel after they both fell for the rich dude at the beginning. IDK-
Also- was she screwing the old lady?