Henry has just learned that his fiancée Carolyn has a twin sister, Laura. While Carolyn leaves town for a few weeks, Laura temporarily moves in to Henry and Carolyn's apartment. Upon Laura's arrival, Henry suspects that Carolyn is testing his fidelity by playing the role of her imaginary twin sister. He immediately starts searching for clues to solve this haunting mystery. Soon, Laura's mind games prove too much for Henry, who can't help but be seduced all over again. In this Hitchcockian psychological thriller, the ultimate commitment is a mysterious gateway into madness.