Open House (2010)

A couple on the verge of a nasty divorce attempts to sell their empty love nest and move on with their lives, separately. Several days after a successful open house, they are horrified to discover that a potential buyer didn't leave their home. While Alice is being held captive in the basement, the unannounced house guest moves in upstairs. She senses that her capture is being kept a rebellious secret. She knows her way out--if only she can get out alive.