Michael Powell directed this groundbreaking study in voyeurism, cinema, and obsession.

When Mark was a child, his father, a highly esteemed professor, used him as a form of laboratory rat in a series of experiments that tested various levels of fear. As an adult, Mark too maintains a fascination with terror, having matured into a psychopathic killer with a penchant for filming women on the verge of death. Since he works as a cameraman for a film studio, he easily indulges his fetish by luring aspiring actresses into isolated areas for "screen tests."

But then Mark meets Helen, a neighbor who wishes to become his friend... and the tormented murderer's downfall begins.