Dans un futur où les Terriens ont enfin réussi à dompter leurs émotions, une équipe de chercheurs est envoyée en observation d'une civilisation humaine découverte sur une autre planète, dont les mœurs et la technologie sont restées aux stades les plus barbares. L'un des observateurs finira par prendre parti contre la règle la plus élémentaire, celle de non-ingérence, pour lutter contre le régime de terreur des obscurantistes.
The story starts as a retrospective, as police officer Dave Speed (Terence Hill) faces his fourth execution attempt (this time by the electric chair) for the alleged murder of his superior and friend, Sergeant Willy Dunlop (Ernest Borgnine). While taking his last walk once more, Dave reminisces about how this all got started.
David Gordon (John Cusack), a popular science fiction author, was widowed when his wife Mary died as they were trying to adopt a child. Two years later, David is finally matched with a young boy named Dennis (Bobby Coleman). Socially awkward, Dennis believes he is from Mars and only goes outdoors when under the cover of a large box to block out the sun's harmful rays. Although initially hesitant to adopt a boy by himself, David recognizes a part of him in Dennis and slowly coaxes him out of the box and into his home.
Kim Sun-yi, an elderly woman in her sixties living in the US, receives a phone call about the sale of her old family home back in South Korea. Returning to her homeland, she's met by granddaughter Eun-joo, and they drive to the house in the country and stay the night. Sun-yi recalls how 47 years ago when she was a teenage girl in 1965, she moved from Seoul along with her widowed mother and sister Sun-ja to a remote valley to undergo a period of convalescence after suffering problems with her lungs. The Kims lived in genteel poverty at the mercy of their arrogant and foppish landlord, Ji-tae, son of the business partner of Sun-yi's late father. Because of her delicate health, the beautiful yet introverted Sun-yi lives an isolated life in the country home, without any friends her age.
Charles is an old retiree who lives in a maid's room in the house of his lover, a rich widow. He is forced out onto the street with his dog after the widow breaks off the relationship, as she decides to marry again. With no home nor way to make money, they wander the streets of Paris.
Les dirigeants de la planète Mars voudraient bien savoir en quoi consiste l'amour, particulier à la planète Terre. Ils dépêchent pour cela un de leurs membres qui va vite comprendre ce qui fait tourner le monde en rencontrant une magnifique terrienne.
Akoba (Robert Brown) leads a hunting party into the hills to search for prey. One member of the tribe traps a warthog in a pit, and then Akoba's son Tumak (John Richardson) kills it. The tribe brings it home for dinner and Tumak is later banished to the harsh desert because of a fight over a piece of meat with Akoba. After surviving many dangers such as a giant iguana, ape men, Apatosaurus and a giant spider, he collapses on a remote beach, where he is spotted by "Loana the Fair One" (Raquel Welch) and her fellow fisherwomen of the Shell tribe. They are about to help him when an Archelon (which is three times the size of the actual prehistoric Archelon) makes its way to the beach. Men of the Shell tribe arrive and drive it back into the sea. Tumak is taken to their village, where Loana tends to him. Scenes follow emphasising that the Shell tribe is more advanced and more civilized than the Rock tribe. They have cave paintings, music, delicate jewellery made from shells, agriculture, and rudimentary language – all things Tumak seems to have never before encountered.
A sixteen-year-old boy who grows up on Mars falls in love with a girl on Earth, whom he has been communicating with, so he starts his journey to see her.
Midvale College is told that a wealthy man, Mr. Astorbilt (Arthur O'Connell), will give a large donation, but he has a strange request — he challenges the school to build a man-powered flying machine. If they succeed by a certain date, they get the donation, otherwise it will go to a rival school.
Astronaut Capt. Richmond Talbot inadvertently volunteers to make the first manned flight around the moon. He is ordered to keep the upcoming moon flight a secret, even from his family. Due to the classified nature of the mission, he is placed under the watchful eye of several national security agencies.
Deux enfants, Meg et le benjamin mais non moins précoce Charles Wallace, vivent avec leur mère scientifique. Leur père, lui aussi scientifique, a mystérieusement disparu depuis 4 ans.
2005 : to convince French people on the interest of space research and its budget, a contest is organised : a scrach game with millions of scratchcards, where the two winners will receive their ticket for space. They must leave for the French orbital station (which only exists for the film and does not exist in reality) with two professional astronauts and a scientist. The adventure will not happen like expected. One of the contestants, who has cheated to obtain the ticket, appears to be once in space, a dangerous madman seeking for revenge.
Ellen Andrews (Barbara Harris) and her daughter, Annabel Andrews (Jodie Foster) constantly quarrel. Following a disagreement on Friday the 13th, Annabel leaves to join a friend at a local diner. In sync, Annabel and Ellen (who is in the family home's kitchen) both wish aloud, "I wish I could switch places with her for just one day." Their wish comes true when they switch their bodies and subsequently lives.
Calvin Fuller is a nerdy young boy living in the Los Angeles suburb of Reseda. The gangly, unsure youth is first seen at a baseball game, standing at bat for his team, the Knights, ready for yet another strike out. Suddenly an earthquake hits; as the others run for safety, the ground opens up under Calvin's shoes and he falls through the chasm. Eventually he lands on the head of a 6th-century black knight. Upon hearing of his miraculous appearance, the elderly King Arthur, seeing him as the savior whose appearance Merlin has predicted, dubs the boy Calvin of Reseda and invites him to dine with the court.