The Skeleton Key

The Skeleton Key hits all the right notes, but it could have been done in half the time.
About a third of the way into the story I realized that they weren't even going to throw red herrings at me, so I stopped paying too much attention and decided to just sit back and mindlessly enjoy the movie. Because of this, I'm not ashamed to say I didn't completely figure out the "surprise ending" before hand. Megan did, but she always does. (She spent half of Mission:Impossible saying, "See? I knew it was him!")
The MTV crowd (this movie's target audience) has been teased with ads saying, "If you haven't seen this movie yet, don't let the cool kids who have ruin it for you by giving away the super-awesome secret surprise ending!" Not dissimilar to the marketing of creature features and horror movies from the 50's and 60's... just not as elaborate.
Don't waste your time on this one. It might qualify as a renter if someone hasn't spoiled the ending for you.
The old lady is the hoodoo woman (she's taken over the body, after having taken over the little girl's body back in the 30's) and the young lawyer is her husband, who used to be in the body of the old man, who's being drugged to stay quiet until the woman can take over the body of the hospice worker girl, which she does.
Now you don't even have to rent it.

http://www.theskeletonkeymovie.com/