Back in the UK, a group of scientists led by Dr. Smiles and the formidable Miss Brunner (who consumes her lovers) try to persuade Cornelius to locate the microfilm containing his father's Final Programme. Jerry learns from his family servant of his sister Catherine's imprisonment at the hands of his evil, drug-addicted brother, Frank; Frank has his and Jerry's sister Catherine held captive in their family home, and has addicted her to drugs for unspecified reasons. Jerry instructs his servant John to smuggle Catherine out to the lodge on the property's grounds; he will take care of Frank. Jerry sets out to rescue Catherine, with whom his relationship is hinted to be one of incest. He consults Major Wrongway Lindbergh, who supplies him with a high-powered jet (not seen onscreen), and also his old friend "Shades" who may be able to supply him with napalm. Norwegian actress and pinup model Julie Ege appears briefly in this scene as Miss Dazzle, a friend of Jerry's. The attack on the old house commences. The house is protected by a sound system which induces pseudo-epilepsy; however Jerry and the others manage to get inside unharmed. They fight their way past many traps including poison gas and a lethal chessboard to be breached. Jerry finds John fatally wounded by Frank; John confesses that Catherine has not been freed and that Frank has returned her to the bedroom, before dying. Jerry finally confronts Frank, and a needlegun fight ensues. In the process, Catherine is accidentally killed by Jerry. Jerry is wounded, and Frank falls into the hands of Miss Brunner. She forces him to open the vaults, but he outsmarts her and gets away.

After Jerry recuperates from being infected by one of Frank's needles, he again meets Miss Brunner, who introduces him to her new friend, Jenny, one of her lovers. They plot to go and find Frank but in the meantime, Jenny, after playing the piano naked in Jerry's flat, is consumed by Miss Brunner. Frank has set up a meeting to sell the microfilm to Baxter (Patrick Magee); Jerry and Miss Brunner track them down. Miss Brunner consumes Dr Baxter. When they find Frank, another fight ensues, and this time Frank is killed. despite having landed in Jerry's jet, Miss Brunner takes Cornelius and they return via hot-air balloon with the recovered microfilm to Lapland, "Daddy's summer resort".

There, the scientists put the Final Programme into operation, in a process that involves combining Miss Brunner with another person to form an hermaphroditic all-purpose human being. At the last minute, Brunner chooses Cornelius over the previously designated participant, Dimitri, who is shot dead by Miss Brunner. The scientists of the project, working against time, scramble to re-calibrate their experiment for Cornelius. He is placed inside a large chamber with Brunner and bathed by solar radiation. Forces are unleashed that kill the scientists. A single being emerges from the chamber - the result of the experiment is supposedly a new Messiah, but is actually a rather dumpy looking caveman who says "Be seein' ya, sweetheart" in imitation Humphrey Bogart accent." Wikipedia