In Montreal, a scientist named André Delambre (David Hedison) is found dead with his head and one arm crushed in a hydraulic press. His wife Helene (Patricia Owens) confesses to having killed him but will not provide a motive and begins acting strangely. She seems to be obsessed with flies and asks everyone to look for a white-headed fly. André’s brother Francois (Vincent Price) claims to have caught the creature and she begins to explain. In the flashback, André, Helene, and their son Philippe (Charles Herbert) are happy. André is working on a matter-transformation device called the disintegrator-integrator, testing it on small objects and then living creatures, including the family cat, which does not re-integrate but can still be heard mewing somewhere. He then builds two chambers big enough for a human being.
Helene goes down to the basement lab to check on him and finds him with a black cloth over his head and a deformity on his left hand. Typing notes to her, he says that he attempted to transport himself, but a fly came into the booth with him and they were combined into one creature. He now has the head and the left arm of a giant fly, and somewhere in the house is a fly with a tiny human head and a left human arm. He asks her to catch the fly so he can reverse the process. She sees it but it slips out of the house through a crack in the window. André is beginning to think and act like a fly and is losing his intelligence. He smashes his equipment in despair, burns his notes and begs her to take him to the factory, where he starts the hydraulic press and gets her to crush his head and arm.
Detective Inspector Charas (Herbert Marshall) believes she is criminally insane. As they are about to take her to the mental hospital, young Philippe tells Francois that he has seen the white-headed fly trapped in a web in the garden. Francois brings the Inspector to the place and they see the fly with André’s head trapped in the web with a spider about to devour him alive. His faint high-pitched scream, “Help me! Help me!” brings them to crush both fly and spider with a rock—one of the most remembered moments in horror-movies. The family lives on and Vincent Price gives the coda, about the search for truth being the most important and the most dangerous work in the world.
The film was produced and directed by Kurt Neumann, from a screenplay by James Clavell of The Great Escape, To Sir with Love, and Shogun fame, based on a short story in Playboy Magazine by George Langelaan. It spawned two sequels—Return of the Fly in 1959 and Curse of the Fly in 1965—and a remake by David Cronenberg with Jeff Goldblum in 1986. The fly’s giant head, built by Ben Nye, weighed twenty pounds and David Hedison said it was practically impossible to act in. Vincent Price recalled that the cast broke up every time they heard, “Help me! Help me!” in a tiny little voice, but the effect on audiences was quite different.
The film received mixed reviews but garnered a nomination for a Hugo and it now has 95% favorable on Rotten Tomatoes. It is a major horror-movie and, with House of Wax and The Tingler, cemented Vincent Price’s status as King of Horror. It was also a hit for director Kurt Neumann, but he died a week before it was released. It was filmed in color but many people remember it in black-and-white, perhaps because that is how they saw it on early TV. It was decided not to show André gradually evolving into the fly because it would have been too disgusting, but the Cronenberg remake seized that idea and ran with it. Betty Lou Gerson, who played the nurse, was the voice of Cruella Deville in 101 Dalmations (1961). The sound for the disintegrator-integrator is the guitar being played backwards used for the Martian heat-rays in War of the Worlds.