Breaking Nikki (2009)

Nikki is a prostitute. Used to meet unusual men in unusual situations, nothing's ever surprising for her. That is, until she meets Devon. While Nikki finds that Devon is not what he seems to be, we learn the story of Susan, Devon's ex wife, who's secretly locked down in his cellar. She wakes up the next morning, she finds herself trapped in Devon's house, forced to become Susan. While Devon becomes more and more obsessed with making Nikki become Susan, David starts falling in love with her as he might have been in love with Susan. Meanwhile, trapped in a locker in the cellar, Susan starts trying to convince David to let her go. It will all lead to one murderous conclusion in the twisted, unexpected finale of Breaking Nikki.