The film begins on New Year's Eve in the middle of the 21st century. After space station Alpha-Two reports impossible "negative radiation" readings and loses contact with United Democracies (U.D.) headquarters, Captain Tice and his crew are sent to investigate. They find the Alpha-Two crew immobilized, some dead, before coming under attack themselves by green glowing energy beings. The creatures immobilize Tice's team and the space station disappears entirely. On space station Gamma-One, Commander Halstead sends ships to investigate the remaining space stations and evacuates all but a skeleton crew. Meanwhile on Earth, the creatures have possessed Captain Dubois and use him to break into the Institute for Advanced Sciences's nuclear reactor. The possessed Dubois sends the U.D. a message offering "symbiotic partnership" for "the good of the whole".
At a dinner party with their wives, NASA scientist Dr. Keith Ritchie (Tony Huston) reveals to his colleague Dr. Curt Taylor (John Agar) that he has secretly been in communication with a three-eyed, bat-winged alien from Venus named Zontar who he claims is coming to Earth to solve all of the world's problems. However, as soon as Zontar arrives on Earth via a fallen laser satellite it quickly becomes obvious that the skeletal black creature has a hidden agenda as it begins causing local power outages that stop telephones, automobiles and even running water from working and it starts taking control of people's minds using flying lobster-like "injecto-pods" that sprout from its wings. Only after his wife is killed does Ritchie finally realize that Zontar has come not as a savior but as a conqueror, and he goes to confront the hideous alien in the sulfur spring-heated cave that it has made its secret base.
Project Star Talk is based at a UK radio telescope site, its mission is to listen for radio signals from other intelligences. Dr. Joe Burke (Simon Oates) is the head of the project assisted by his small team consisting of electronics expert Ben Keller (Stanley Meadows) and office manager Sandy Lund (Zena Marshall). Due to the lack of success reported by the Site Manager, Dr. Henry Shore (Max Adrian), Project Star Talk is given 90 days in order to report positive results. During this period an accountant, Mr. Yellowlees (Charles Hawtrey) is sent to look over the project's accounts. As luck would have it, a repeating signal is received by the project, but the signal is only coming from a small asteroid with no atmosphere in the outer Solar System. Despite this, Dr. Burke spends the balance of his grant to equip the telescope with a powerful transmitter to contact the source of the signals. The night of the transmission, Mr. Yellowlees and Mrs. Jones (Patricia Hayes) who runs the tea trolley, stay to witness this historic event. While waiting for a response, Dr. Burke tells of his father's discovery at an archaeological dig in France of a cube that gave him strange dreams as a boy, inspiring him to become an astronomer. The signal is sent and reaches the asteroid. The asteroid has on it a huge installation that receives the radio signal and answers it with a spaceship sent riding down the radio beam to the point of transmission. When the spacecraft arrives at Project Star Talk, it picks up the transmitter shed and carries it, the project staff and the 2 witnesses to the alien installation. The telescope staff's leader believes, despite eyewitnesses that the transmitter shed exploded, killing the Star Talk team.
On April 12, 1961, Soviet cosmonaut Yuri Gagarin blasted off in a Vostok rocket, becoming the first human in space and orbiting Earth for 108 minutes. He was one of the first group of cosmonauts who were selected from over three thousand fighter pilots throughout the Soviet Union.
In the late 1960s, astronauts training in an Apollo simulator have their session ended early. They grumble about it, but their commander, Chiz (Robert Duvall), knows the reason for the abort: the Pilgrim Program. The Russians will be sending a moon landing mission up in four weeks. The Americans had a secret alternate plan to the Apollo program (Pilgrim) in case this happened. One man would be sent to the moon in a one-way rocket, a modified Project Gemini craft. He would stay on the moon for a few months in a shelter pod launched and landed before him. Later, a manned Apollo mission would come to retrieve him.
Astronauts landing on Venus encounter dangerous creatures and almost meet sexy Venusian women. The astronauts kill a creature that is worshiped by the Venusian women who then attempt to use their powers of nature to kill the astronauts but fail. At last, the astronauts leave the planet and their robot that was burnt by the volcano fire is placed as a god by the Venusian women who have already destroyed the statue of their previous god (a bird).
Dr. Kris Kelvin arrives on Solaris Station, a space station orbiting the ocean planet of Solaris. The scientists there have been studying the planet and its ocean for many decades. Shortly before Kelvin's arrival, the crew exposed the ocean to a high-energy gamma-ray bombardment. The ocean's response tests the scientists' minds by confronting them with their most painful thoughts and memories. The ocean does this by materializing physical human simulacra. Kelvin confronts memories of his dead lover and guilt about her suicide. The torments of the other researchers are only suggested but seem even worse than Kelvin’s personal ordeal. The ocean’s intelligence expresses physical phenomena in ways difficult for their limited science to explain, deeply upsetting the scientists. The alien mind of Solaris appears to differ so much from the human mind that communication doesn't seem possible.
A spy (Essie Lin Chia) discovers that the Chinese government has created a doomsday device (the "key" to which, "only Chairman Mao has") capable of destroying the Earth and it will be activated in 72 hours. Soon after, Astra – a two year return mission to Venus by the United States Space Program – has its time of launch speeded up and half of the male flight crew are replaced by women shortly before take-off, including one Russian. Shortly before blastoff military alerts are put into effect.
Psychologist Kris Kelvin (Donatas Banionis) spends his last day on Earth reflecting on his life while walking by a lake near his childhood home where his elderly father still resides. Kelvin is about to embark on an interstellar journey to a space station orbiting the remote oceanic planet Solaris. After decades of study, the scientific mission at the space station has barely progressed. The crew is sending confusing messages. Kelvin is dispatched to evaluate the situation aboard the ship and determine whether the venture should continue.
Exploring ice caves on the moon, crew members carry a strange fungus back to their space station. After a meteor strike disables the station, the fungus begins to overrun the ship.
Sun Ra, who has been reported lost since his European tour in June 1969, lands on a new planet in outerspace with his crew "The Arkestra" and decides to settle African Americans on this planet. The medium of transportation he had chosen is music. He travels back in time and returns to the Chicago strip club where he used to play piano with the name "Sonny Ray" in 1943. There he confronts The Overseer (Ray Johnson), a pimp-overlord, and they agree on a duel at cards for the fate of the Black race. Each card drawn is a minor goal to achieve for Ra or The Overseer which will determine the winner of the duel. Then, to present time, Ra disembarks from his spaceship at Oakland and tries to spread his word by meeting with young Blacks at an Oakland youth centre and opening an "employment agency" to recruit people eager to move to the planet. He also agrees with Jimmy Fey (Christopher Brooks), the minion of The Overseer, to arrange radio interviews, a record album, and eventually a concert that will help him dictate his message. At the end, Ra takes Fey's "Black parts" with him to the spaceship, leaving him with his White parts. Fey, now acting white, leaves The Overseer who loses the duel. The planet Earth is destroyed after Ra's spaceship flies into space.
The film begins with the text "Meanwhile — in another part of the galaxy — later that same day". A household steam iron flies through space, fleeing a toaster, which fires toast at it. Two robots named 4-Q-2 (who looks like the Tin Man from the 1939 film The Wizard of Oz) and Arty-Deco (a canister vacuum cleaner), escape from the evil Empire. After launching from the ship (a cassette player) in an escape pod (a cassette tape), they land on a desert planet (a watermelon). They are found by young Fluke Starbucker (played by future multi-platinum award-winning music producer Scott Mathews) who finds a video message saved on Arty-Deco. It is a loop of Princess Anne-Droid saying "Help me, Augie Ben Doggie, you're my only hope." Upon meeting Augie "Ben" Doggie (of the venerable Red-Eye Knights), Fluke receives his father's lightsaber (a flashlight). After tricking the Imperial Steam Trooper guards (steam cabinets) to let them into the city, they reach a cantina, which Fluke describes as "too weird". The cantina is a country-and-western bar, where they meet space-renegade Ham Salad and Chewchilla the Wookiee Monster (played by a puppet that resembles Cookie Monster of Sesame Street fame). Meanwhile, the villainous Darph Nader (whose name could be in reference to outspoken consumer advocate Ralph Nader) is interrogating the princess. When she refuses to talk (mainly because she can't understand him; his speech is muffled by his welder's mask), he destroys her peaceful home planet, Basketball (the name speaks for itself).
After a mechanical failure aboard the spaceship Odyssey, Captain Lee Norsythe (Louie Lawless) is forced to crash land on a planet with atmosphere and conditions much like that of Earth, although it is many light-years away. As the ship sinks into the lake that it landed in, communications officer Cindy (Mary Appleseth) realizes that she forgot the radio in the ship and attempts to retrieve it, with the assistance of fellow crew-member Chuck (Chuck Pennington). En route, Cindy is attacked and killed by an unidentified aquatic creature, prompting Chuck to return to shore without the radio.
The five-year mission seen in The Original Series has finished, and the crew has moved on from the Enterprise. Captain James T. Kirk has been promoted to Admiral, Doctor Leonard McCoy has left Starfleet to become a veterinarian while other members of the crew have been given desk jobs. This has led engineer Montgomery Scott to become an alcoholic through boredom. Spock had returned to the planet Vulcan where he was seeking to control his human half.