This sequel to Kurt Neumann's The Fly (1958) is peculiar, to say the least. Producer/director Neumann had passed away during the summer of 1958, and the studio needed a sequel. The resulting film, Return of the Fly, was directed by Edward L. Bernds, a filmmaker (and former sound man at Columbia Pictures) most closely associated with the Three Stooges, but who had lately moved successfully into popular science fiction, with movies such as World Without End, Space Master X-7, and Queen of Outer Space to his credit -- not that this last, in particular, seemed to qualify him for anything but tongue-in-cheek satire. Curse of the Fly was shot in CinemaScope but in black-and-white, an unusual combination that is usually associated with artier movies, as a compromise for discriminating directors who can't avoid the widescreen format but want to present something serious; in this particular case, however, it was purely a budgetary decision. Vincent Price is the nominal star as Francois Delambre, the brother of Andre Delambre, who died as a result of his experiments with a matter transmitting device in The Fly. It is now a dozen years later, and Andre's son, Philippe (Brett Halsey), has just laid his mother to rest, having witnessed the final years of her life blighted by the memory of the horror of Andre's death. He convinces Francois to tell him what happened and of the device that destroyed his parents' happy life together. Philippe vows to perfect the matter transmitter, so that all of the heartache and sacrifice by his parents will not have been in vain. He employs as his assistant a scientist friend, Alan Hinds (David Frankham), who, unbeknownst to him, has shady business connections and a dark secret in his own past. Alan conspires to steal the secret of the matter transmitter, but first he must dispose of a detective who has come to arrest him for an earlier crime, and then eliminate Philippe, who doesn't know what Alan has done, only that he's hiding something. Thus, the same disaster that befell Philippe's father now occurs again, to him -- his body parts are transposed with those of a house-fly. The human-sized fly, even nastier looking than the monster in the original film, goes on a rampage, trying to catch Alan and get revenge for what has happened to him, using what faculties he has. Meanwhile, Francois gets help from the surviving detective on his brother's case, who knows the truth, and the two try to trap the monster alive and also find the fly-sized creature with Philippe's head and features, so they can try and unscramble the atoms of both.
by Bruce Eder synopsis