Margot Kidder is Danielle, a beautiful model separated from her Siamese twin, Dominique.

When a hotshot reporter (Jennifer Salt) suspects Dominique of a brutal murder, she becomes dangerously ensnared in the sisters' insidious sibling bond.

A scary and stylish paean to female destructiveness, Brian De Palma's first foray into horror voyeurism is a stunning amalgam of split-screen effects, bloody birthday cakes, and a chilling score by frequent Hitchcock collaborator Bernard Herrmann.