I Married a Monster from Outer Space

Aliens arrive on Earth to possess the bodies of humans. One of their first victims is a young man, whose new wife soon realizes something is wrong with him.
Aliens from Outer Space are slowly switching places with real humans -- one of the first being a young man about to get married. Slowly, his new wife realizes something is wrong, and her suspicions are confirmed when her husband's odd behaviour begins to show up in other townspeople.