The movie takes place in the year 2079. Forty-five years earlier, Earth was attacked by a hostile and implacable alien civilization from Alpha Centauri. Force shield domes are put in place to protect cities, and a totalitarian global military government is established to effect the war and the survival of humans. The Centaurians have never been physically seen.
Ce film fait suite au premier.
Depuis 20 ans les nations du monde ont travaillé ensemble sur un important programme de défense colossal fondé sur la technologie extraterrestre récupérée lors de la première invasion sous la supervision de David Levinson qui est désormais le directeur de la défense spatiale. Les forces armées de la Terre comptent maintenant des chasseurs équipés de canons lasers, des satellites de défense et des bases de défenses sur la Lune et sur Rhéa équipées des mêmes super lasers utilisés par les extraterrestres pour détruire les villes dans le premier opus.
On July 2, a 500 km wide alien mothership enters Earth's orbit and deploys several dozen saucer-shaped "destroyer" spacecraft, each 15 miles (24 km) wide. As they take position over some of Earth's major cities, David Levinson (Jeff Goldblum), an MIT graduate working for a cable company in New York City, discovers hidden transmissions in Earth's satellites which he realizes is a timer counting down to a coordinated attack by the aliens. With the support of his estranged wife Constance Spano (Margaret Colin), the White House Communications Director, he and his father Julius (Judd Hirsch) gain entrance into the Oval Office to notify President Thomas J. Whitmore (Bill Pullman) about the attack. Whitmore orders large-scale evacuations of the targeted cities, but the aliens attack with advanced directed-energy weapons before these can be carried out. Whitmore, portions of his staff, and the Levinsons narrowly escape aboard Air Force One as Washington, D.C. is destroyed.
After the space shuttle Patriot crashes on Earth, a fungus-like alien lifeform is discovered on the remaining parts scattered over US territory. Once people come into contact with the organism, they are controlled by it when they enter REM sleep. One of the first people infected is Tucker Kaufman, a CDC director investigating the crash.
A group of pilots in the Canadian wilderness begin to hear strange reports over their radios about planes crashing, cars stalling, and a deadly plague which has gripped the planet. As the plot continues, it's clear that Earth is in the midst of an invasion. The pilots barracade themselves in a cabin in the woods and wait for impending doom.
An unemployed drifter named John Nada (Roddy Piper) finds construction work in Los Angeles, and befriends fellow construction worker Frank Armitage (Keith David), who leads him to a local shantytown soup kitchen. There, Nada encounters strange activity around the church: a blind preacher (Raymond St. Jacques) loudly chastising others to wake up, a police helicopter scouts them overhead, and a drifter (George Buck Flower) complains that his TV signal is continually interrupted by a man warning everyone about those in power. Nada discovers the nearby church is a front; the choir heard outside is an audio recording and the building is filled with scientific equipment and cardboard boxes. Nada finds a box hidden in the wall, but flees when the preacher notices him. That night, the police attack and bulldoze the shantytown. Nada returns in the morning to find the church empty, but with the hidden boxes still in the wall. He takes one of the boxes and in an alley, he opens the box and finds it filled with sunglasses. Taking a pair, he hides the box in a garbage can.
A flying saucer lands in the woods. A teenage couple, Johnny Carter (Terrell) and Joan Haydon (Castillo), while driving to their local lover's lane without the headlights on, accidentally run down one of the saucer's large-headed occupants.
In the 1960s, two astronauts, Fuji and Glenn, are sent to investigate the surface of the mysterious "Planet X". There they encounter advanced and seemingly benevolent human-like beings called the Xiliens and their leader The Controller. The aliens usher the astronauts into their underground base, and moments later the surface is attacked by a creature the Xiliens call "Monster Zero", but which the astronauts recognize as King Ghidorah, a planet-destroying monster that had attacked Earth once before. The monster eventually leaves, but the Controller states that Ghidorah has been attacking repeatedly, forcing them to live underground in constant fear. He requests to borrow the Earth monsters Godzilla and Rodan to act as sentries against Ghidorah's attacks, in return for the cure for cancer (the English dub says the formula can cure any disease). The astronauts return to Earth and deliver the message.
Dr. Tom Anderson (Lee Van Cleef), an embittered scientist, has made contact with Zontar, a Venusian creature, while using his radio transmitter. The alien's secret motivation is to take complete control of the Earth by enslaving humanity using mind control devices; the alien claims it only wants to bring peace to our troubled world by eliminating all emotions. Anderson agrees to help the creature and even intends to allow it to assimilate his wife (Beverly Garland) and friend Dr. Nelson (Peter Graves).
A huge, blinking flying saucer that's approaching the Earth emits a glowing object. This object races ahead of it to intercept a man who's driving down a lonely road. It takes over the man's body and directs him to Central Labs, a U.S. research facility that's been tracking the saucer (supposing it to be an asteroid).
The Film opens with climatologist Ilana Green (Lindsay Crouse) examining a poppy field and remarking that it "shouldn't be here". We then see that the poppy field is in the middle of the Arctic.
The film begins in 1985, when engineers involved in an industrial project to irrigate the Gobi Desert accidentally unearth a mysterious and apparently artificial "spool". When found to be made of a material unknown on Earth, the spool is circumstantially linked to the Tunguska explosion of 1908. The "spool" is seized on as evidence that the explosion, originally blamed on a meteor, was actually caused by a spaceship. Professor Harringway deduces the alien craft must have come from Venus. The spool itself is determined to be a flight recorder, and partially decoded by an international team of scientists led by Professor Sikarna and Dr. Tchen Yu. When radio greetings sent to Venus go unanswered, Harringway announces that a journey to Venus is Earth's only alternative. The recently completed Soviet spaceship Cosmostrator I (Kosmokrator in the original), intended to voyage to Mars, is redirected to Venus, a 30–31 day trip. During the voyage, Sikarna works furiously to translate the alien message on the disc using the ship's computer.
In deep space, a race of gelatinous creatures abandon their dying world. Pushed through space by the solar wind, they make their way to Earth and land in San Francisco. Some fall on plant leaves, assimilating them and forming small pods with pink flowers. Elizabeth Driscoll (Brooke Adams), an employee at the San Francisco Health Department, is one of several people who bring the flowers home. The next morning, Elizabeth's boyfriend, Geoffrey Howell, DDS (Art Hindle), suddenly becomes distant, and she senses that something is wrong. Her colleague, health inspector Matthew Bennell (Donald Sutherland), suggests that she see his friend, psychiatrist Dr. David Kibner (Leonard Nimoy). While driving to a book party Kibner is attending, they are accosted by a hysterical man (Kevin McCarthy, in a direct homage to the original film). The man runs off, and is soon seen dead, surrounded by a crowd of emotionless onlookers. At the party, Matthew calls the police about the incident, and finds them strangely indifferent. An agitated party attendee starts declaring that her husband is not her real husband. Kibner works to reconcile them. He also suggests that Elizabeth wants to believe that Geoffrey has changed because she is looking for an excuse to get out of their relationship.
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: