When medical student Marty Hiller (Justine Bateman) places an ad for a roommate, her ad is answered by handsome, clean-cut Alec Danz (Adam Baldwin). At first Alec seems to be a wonderful roommate; supportive, considerate and a real friend. However, Alec's affection turns to obsession as he plots to manipulate and control all aspects of Marty's life, imprison her in her own apartment and make her his.