The Fly (1958)

"If she looked upon the horror her husband had become...She would scream for the rest of her life!"

Industrialist François Delambre is called late at night by his sister-in-law, Helene, who tells him that she has just killed her husband. Reluctant at first, she eventually explains to the police that he invented a matter transportation apparatus and, while experimenting on himself, a fly entered the chamber.