A woman advertising for a new roommate finds that something very strange is going on with the tenant who decides to move in.

[last lines]
Allison Jones: [voice-over] I cried the whole week of Sam's funeral. Graham says that it won't bring him back. He said that I should start letting go. He's right. Hedy's parents said that for years they tried to explain to her that her sister's death wasn't her fault. She never forgave herself for surviving. So, every day I try to forgive Hedy for killing Sam. Then, I try to do what she couldn't: forgive myself for killing her. I know it can happen to someone who doesn't.
Hedra Carlson: Well, he will cheat on you again - that's a promise. And when he does, don't come crying to me, because... I've had it with you. You're so FUCKING weak!
Allison Jones: I know you weren't yourself when you did this, Hedy.
Hedra Carlson: I know. I was YOU.
Hedra Carlson: You know, identical twins are never really identical. There's always one whose prettier... and the one whose not, does all the work... She used me, then she left me - just like you.
Hedra Carlson: [looking for Allison] Ally? Ally, come out of hiding now! I'm scared!
Hedra Carlson: [pointing a gun at Allison] Ally, don't move! Come back here! Don't make me shoot you!
Allison Jones: I'm not your sister, Hedy. I'm nothing like your sister! Not anymore!
Graham Knox: I can be butch when I have to, I get it from my mother.