Beverly and Elliot Mantle (Jeremy Irons) are twin gynecologists, identical in looks but with very different natures. The suave Elliot seduces his patients first, then passes them along to the bookish Beverly. When Claire (Bujold), a celebrated actress, comes to see them, Beverly is drawn to her, and they begin a relationship. When Claire discovers the twins’ unusual arrangement, she breaks up with Beverly, who then descends into pill-popping psychosis. Can his brother bring him back from the brink of madness?

Canadian horror maestro Cronenberg (“Videodrome”) crafts a twisty, stylish, medical thriller that grabs you and never lets go. Using then-groundbreaking split-screen technology, he presents two distinctly separate characters whose minds and bodies eventually merge in a gruesome clash of parasitic symbiosis. Irons gets maximum credit for imbuing the twins with such differing traits, making each character totally believable and completely distinct. His performance alone makes this fascinating, disturbing picture worth your time and attention.