The third installment of the science fiction series that began with the classic 'The Fly' (1958). The film's plot again revolves around the Delambre family, although this time it is the original scientist's son, Henri Delambre (Brian Donlevy), who becomes obsessed with transporter experiments to the dismay of his two sons, who want to live normal lives and forget about their grandfather's invention. Henri's oldest son, Martin (George Baker), marries a young woman who just escaped from a mental hospital. After Martin's new wife discovers a closet filled with deranged humans left over from failed teleportation experiments, the police are called and Henri attempts to flee using the infamous transporter.