RETURN OF THE FLY

After Hélène Delambre passes away, her son, Phillipe Delambre, now an adult, is determined to vindicate his late father by successfully completing the experiment he had worked on. His paternal uncle François refuses to help. Phillipe hires Alan Hinds from Delambre Frere and uses his own finances, but the funds run out before the equipment is complete. When Phillipe threatens to sell his half of Delambre Frere, François relents and funds the completion. After some adjustments, they use the transporter to "store" and later re-materialize test animals.

Alan Hinds turns out to be Ronald Holmes, an industrial spy. Holmes tries to sell the secrets to a shadowy cohort named Max. Before Holmes can get away with the papers, a British agent confronts him. Holmes knocks him out and uses the transporter to "store" the body. When rematerialized, the agent has the paws of a guinea pig that had been disintegrated earlier, and the guinea pig has human hands. Holmes kills the rodent and puts the dead agent in his car, which he sends into the Saint Lawrence River.

Phillipe confronts Holmes about all the oddities, with a fight ensuing and Phillipe being knocked out. Holmes hides Phillipe the same way he did the agent, but in a twist of malice he catches a fly and adds it to the transporter with him. François re-materializes Phillipe, but with a giant fly head, arm, and leg (whereas the tiny fly has his head, arm, and leg). The fly-headed Phillipe runs into the night, tracking down and killing Max. He waits for Holmes to arrive and kills him, too, then returns home, where Inspector Beauchamp has found and captured the Phillipe-headed fly. Both are placed in the device together and successfully reintegrated, restoring Phillipe to his normal human form.

Philippe is transformed into a human-fly hybrid after a malicious act by the industrial spy, but is ultimately restored to normal when both he and the mutated fly are reintegrated in the device.

The ending ties up the narrative by restoring Philippe's humanity through scientific means, highlighting both the peril and possibility inherent in unchecked experimentation. Retribution is exacted on the film's antagonists, while the Delambre legacy is given a second chance. It's a finale that underlines the recurring motif of science as both curse and cure in the Delambre saga.