Psychiatrist Dr. Hill is called to the emergency room of a hospital, where a screaming man is being held in custody. Dr. Hill agrees to listen to his story. The man identifies himself as doctor, and he recounts, in flashback, the events leading up to his arrest and arrival at the hospital:
When he accidentally takes possession of a top-secret invisibility potion while en route to his wedding, government bureaucrat Sam Cooper (Steve Guttenberg) finds himself engulfed in a madcap free-for-all as Russians and other bad guys try to get the substance. To elude the Reds, his own State Department bosses and his livid fiancée, Cooper takes the vanishing juice himself—which only makes matters worse.
The inhabitants of the British village of Midwich suddenly fall unconscious, as does anyone entering the village. The military establishes a cordon around Midwich and sends in a man wearing a gas mask, but he, too, falls unconscious and is pulled back with rope. The man awakens and reports experiencing a cold sensation just before passing out. The pilot of a military reconnaissance plane is contacted and asked to investigate. When he flies below 5,000 feet, he loses consciousness and the plane crashes. A five-mile exclusion zone around the village is established for all aircraft. The villagers regain consciousness and apparently are unaffected.
At University of Zurich Institute of Medicine in Switzerland, Herbert West brings his dead professor, Dr. Hans Gruber, back to life. There are horrific side-effects, however; as West explains, the dosage was too large. When accused of killing Gruber, West counters: "I gave him life!"
On a stormy night, Percy Bysshe Shelley (Douglas Walton) and Lord Byron (Gavin Gordon) praise Mary Shelley (Elsa Lanchester) for her story of Frankenstein and his Monster. Reminding them that her intention was to impart a moral lesson, Mary says she has more of the story to tell. The scene shifts to the end of the 1931 Frankenstein.
In early 1950s southern California, Dr. Clayton Forrester (Gene Barry), a scientist who had worked on the Manhattan Project, is fishing with colleagues when a large object crashes near the town of Linda Rosa. At the impact site, he meets Sylvia Van Buren (Ann Robinson) and her uncle, Pastor Matthew Collins (Lewis Martin). Van Buren was told that the meteorite came down at a low angle, while Forrester observes it appears far lighter than normal for its massive size. His Geiger counter also detects it is slightly radioactive, but the object is still too hot to examine closely. Unable to account for these anomalies, Forrester is intrigued and decides to wait in town overnight for the object to cool down.
In the future, a totalitarian government employs a force known as Firemen to seek out and destroy all literature, permitting them to search anyone, anywhere, at any time. One of the Firemen, Guy Montag (Oskar Werner), meets one of his neighbors, Clarisse (Julie Christie), a 20-year-old schoolteacher whose job is hanging by a thread due to her unorthodox views. The two have a discussion about his job, where she asks if he ever reads the books he burns. Curious, he begins to hide books in his house and read them, starting with Charles Dickens' David Copperfield. This leads to conflict with his wife, Linda (also played by Julie Christie), who is more concerned with being popular enough to be a member of The Family, an interactive television program that refers to its viewers as cousins.
Big and burly African-American soldier Eddie Turner (Joe De Sue) stepped on a land mine while serving in Vietnam and lost both arms and legs. His physicist fiancee Doctor Winifred Walker (Ivory Stone) thinks she's found help for him in her white former teacher and colleague Doctor Stein (John Hart) who has recently won a Nobel Peace Prize for "solving the DNA genetic code".
Dr. Alex Harris (Fritz Weaver) is the developer of Proteus IV, an extremely advanced and autonomous artificial intelligence program. Proteus is so powerful that only a few days after going online, it develops a groundbreaking treatment for leukemia. Harris, a brilliant scientist, has modified his own home to be run by voice activated computers. Unfortunately, his obsession with computers has caused Harris to be estranged from his wife, Susan (Julie Christie).
A United States Air Force crew is dispatched by General Fogerty (David McMahon) from Anchorage, Alaska at the request of Dr. Carrington (Robert Cornthwaite), the chief scientist of a North Pole scientific outpost. They have evidence that an unknown flying craft crashed nearby, so Reporter Ned Scott (Douglas Spencer) tags along for the story.
Set in the American Southwest, Doc (Raphael Sbarge) is an alcoholic security watchman protecting digging equipment from environmental activists, though he befriends one of them named Thrush (Jennifer Runyon). Meanwhile, Dr. Jane Tiptree (Diane Ladd) of the Eunice Corporation is breeding a strain of extra large and fertile chickens by splicing their DNA with that of crocodiles, iguanas, albatrosses, vultures, pelicans, turkeys and ostriches. Unknown to the Corporation's sponsors however, Tiptree is impregnating several of the chickens with dinosaur DNA. One of her resulting creatures, a Deinonychus, escapes and kills the activists, as well as other civilians. Doc investigates and discovers that Tiptree is also creating a virus which causes women to fatally conceive baby dinosaurs, in order to wipe out humanity and thus allow Carnosaurs and Raptors to reclaim the Earth as their own. Tiptree dies giving birth to a baby raptor. After narrowly escaping a Tyrannosaurus and the lab, Doc takes Thrush to a house to recover and injects a serum to cure her. Doc battles the Tyrannosaurus with a skidsteer (an action that was repeated in the fourth sequel) before impaling it. The government infiltrates the community in order to "sterilize" the situation by shooting all the civilians, infected or not. Thrush dies from the virus, meaning that the serum did not work. Doc is shot and killed by government soldiers, who then burn his and Thrush's bodies.
Dr. Cal Meacham (Reason), a noted scientist and jet pilot, is sent an unusual substitute for electronic condensers that he ordered. Instead, he receives instructions and parts to build a complex communication device called an interocitor. Although neither Meacham nor his assistant Joe Wilson (Robert Nichols) have heard of such a device, they immediately begin construction. When they finish, a mysterious man named Exeter (Morrow) appears on the device's screen and tells Meacham he has passed the test. His ability to build the interocitor demonstrates that he is gifted enough to be part of Exeter's special research project.
An eager scientist (John Carradine) tests his new formula for invisibility on an escaped fugitive (Jon Hall). When the formula works the criminal runs off to terrorize a family he believes cheated him out of a fortune years earlier.
In 1964, the United Nations (UN) has launched a rocket flight to the Moon. A multi-national group of astronauts in the UN spacecraft land on the Moon, believing themselves to be the first lunar explorers. They discover a British Union Jack on the surface and a note naming Katherine Callender, claiming the Moon for Queen Victoria. Attempting to trace Callender, UN authorities find she has died, but find her husband Arnold Bedford now an old man in an old people's home. The nursing home staff do not let him watch television reports of the expedition because, according to the matron, it "excites him", dismissing his claims to have been on the Moon as insane delusion. The UN representatives question him about the Moon and he tells them his story. The rest of the film, as a flashback, shows what Bedford and Professor Cavor did in the 1890s.