Remember that scientist that was trying to perfect a matter transportation machine but got fused with a fly when one of the little critters got into the transporter with him? Well, this story is about three of his descendents (a son, Henri Delambre, played by Brian Donlevy and two grandsons). Seems the son wants to continue and perfect the machine while his two sons want to get out of the scientist business and live "normal" lives. The oldest son, Martin, decides to take a wife (who just happens to have escaped from a mental hospital after her parents died). Martin's father is not happy with this intrusion but finally gives in because he understands him son's needs. They all try to be a happy family until humans used in botched experiments are discovered by the new bride and the police nearly discover the lab while looking for Martin's wife. Everyone tries to get out of there via the transporter but things just don't go according to plan ...

For the past three generations the Delambre family has been attempting to disintegrate matter in one place (Montreal) and then transport and reintegrate it in another locale (London). Young Martin Delambre has just married Patricia Stanley, unaware that, though sane, she is an escapee from a mental institution. While staying at the Delambre Canadian estate with Martin and his father, Henri, Patricia begins to doubt her sanity. She learns not only of the ghastly experiments but also that Martin's former wife and two laboratory assistants are locked in the stables--all victims of the Delambres' past failures, which have left them part human and part fly. The experiments have also afflicted Martin with a mysterious recurring malady. Meanwhile, Wan, the Chinese housekeeper, persecutes Patricia because she has usurped the place of Martin's first wife, Judith. When police investigating Patricia's disappearance arrive at the estate, Henri decides that all the residents must be "teleported" to London. However, Martin's brother Albert destroys the London receiving equipment, and Henri becomes lost in the fourth dimension. Having no antidote serum, Martin takes on the metabolism of a fly, and his brief life span expires just as Patricia is rescued by the police.