British botanist Dr. Charles Decker (Michael Gough) goes insane after he discovers a serum that turns his chimpanzee subject Konga into a ferocious gorilla-sized ape. To further his hideous experiments, Dr. Charles Decker mesmerizes the chimp and sends it to London to kill all his former enemies. Among his targets is Dean Foster (Austin Trevor) Professor Tagore (George Pastell) and Bob Kenton (Jess Conrad), the lover of Sandra Banks (Claire Gordon), the woman the doctor wants for himself.
Captain Joe Ryan is salvaging for treasure off the coast of Ireland, when a volcano erupts, nearly sinking his ship. Ryan and his first officer, Sam Slade, take the ship to Nara Island for repairs. As they enter harbour, they discover the floating carcasses of marine animals, the first hint that something dangerous was awoken by the volcano eruption.
In the Florida Everglades, a pair of larger-than-human, intelligent leeches are living in an underwater cave. They begin dragging local people down to their cave where they hold them prisoner and slowly drain them of blood.
American scientist Steve Karnes (Gene Evans) delivers a speech to a British scientific society, headed by Professor James Bickford (André Morell), about the dangers to marine life posed by nuclear testing. Before Karnes can return to the U.S., a real-life example of his concern materializes when Tom Trevethan (Henri Vidon), an old fisherman, receives a lethal doze of radiation; his dying word is "behemoth". Later thousands of dead fish are washed ashore.
The movie opens with a young couple parked in a bleak, rural locale overlooking a ravine. A giant gila monster attacks the car, sending it into the ravine and killing the couple. Later, some friends of the couple decide to assist the local sheriff (Fred Graham) in his search for the missing teens. Chase Winstead (Sullivan), a young mechanic and hot rod racer, locates the crashed car in the ravine and finds evidence of the giant lizard. However, it is only when the hungry reptile attacks a train (a model train set substituted as a low-budget effect) that the authorities realize they are dealing with a (roughly) 70-foot poisonous lizard. By this time, emboldened by its attacks and hungry for prey, the creature attacks the town. It makes straight for the local dance hall where all the teenagers had gathered for a sock hop. However, Chase packs his prized hot rod with nitroglycerin and rigs it to speed straight into the monster, terminating the lizard in a fiery explosion and heroically saving the town.
Captain Thorne Sherman and first mate Rook Griswold deliver supplies by boat to a group on a remote island. The group, consisting of scientist Marlowe Cragis, his research assistant Radford Baines, the scientist's daughter Ann, her recent fiancé Jerry Farrel, and a servant Mario, welcome the captain and his first mate, but subtly resist the visitors staying overnight, even though a hurricane approaches. Thorne goes with the group to their compound. Griswold stays with the boat, to come ashore later.
During one long night in a small rural Pennsylvania town in July 1957, teenager Steve Andrews (Steve McQueen) and his girlfriend, Jane Martin (Aneta Corsaut), are kissing on a lovers' lane when they see a meteor crash beyond the next hill. Steve decides to look for it. An old man (Olin Howland) living nearby finds it first. When he pokes the meteorite with a stick, it breaks open, and the small jelly-like blob inside attaches itself to his hand. In pain and unable to scrape or shake it loose, the old man runs onto the road, where he is nearly struck by Steve's car. Steve and Jane take him to Doctor Hallen (Stephen Chase).
A monomaniacal scientist, Dr. Laird (played by Alec Mango), has invented ultra-sensitive magnetic fields, which attracts objects from space. Strange things begin happening, including a freak storm, and insects and spiders mutate into giant monsters. An alien spaceship appears over London and mankind is warned against the dangers of this scientific experiment.
Jack Flynn is driving down a highway at night, looking at a bracelet he has bought his daughter for her birthday. Suddenly he hits something and his vehicle crashes. The next morning, his teenage daughter Carol, is concerned her "bad-dog" father didn't come home last night. She convinces her boyfriend Mike to assist in a search for her father. They find his crashed truck and the bracelet, but not his body. Thinking he crawled into a nearby cave, they investigate. In the cave they fall onto the gigantic orb web of an enormous spider, a Mexican redleg tarantula, which emerges from behind some rocks to get them. They manage to escape and make it back to town.
On a Swiss mountain, one of three student climbers is killed, his head ripped from his body. Two sisters, a London mind-reading act, are traveling by train to Geneva when one of them, Anne Pilgrim (Janet Munro), faints as they pass the same mountain. Upon waking, she knows that there is something very wrong, so she decides they should get off at the very next stop, Trollenberg.
A rare species of butterfly native to Siberia is found in a mysterious valley in Japan, a pair of entomologists go to investigate. In response, an expedition is dispatched to their habitat, located along the Kitakami River, to discover why the insects might be living in Japan. Two members of the scientific community helm the expedition, but are mysteriously crushed by something that the police can only describe as "powerful." The nearby villagers of the Kitakami River insist that the deaths were a result of the wrath of their mountain god Baradagi-Sanjin.
Off the coast of a small Sicilian fishing village, two fishermen watch in amazement as a spaceship pierces the skies and crashes into the sea. The men, Mondello (Don Orlando) and Verrico (George Khoury), row out to the site and pull two space travelers from the capsized craft before it shudders and sinks into the sea. Meanwhile, in Washington, D.C., General A. D. McIntosh (Thomas Browne Henry) discovers that the government's missing spacecraft, piloted by Col. Bob Calder (William Hopper), has been located off the coast of Italy. As McIntosh flies to Italy, Pepe (Bart Braverman), a little boy who lives in the fishing village of Gerra, finds a metal capsule that has washed up on the beach. Upon opening the capsule, he finds a jelly-like glob inside and sells it to Dr. Leonardo (Frank Puglia), a visiting zoologist who is studying sea creatures. Meanwhile, Leonardo's medical-student granddaughter Marisa (Joan Taylor) is summoned to town to take care of the injured Calder and his companion, Dr. Sharman. When Calder regains consciousness, he finds Sharman in the last throes of the fatal disease that decimated his crew.
Figée dans les glaces de l'Antarctique depuis la préhistoire, une mante religieuse géante est libérée à la suite de la brisure d'un iceberg. Le monstre attaque alors New York, puis Washington. L'armée va devoir stopper l'insecte.
Mitch MacAfee (Jeff Morrow), a civil aeronautical engineer, while engaged in a radar test flight near the North Pole, spots an unidentified flying object. Three jet fighter aircraft are scrambled to pursue and identify the object but one aircraft goes missing. Officials are initially angry at MacAfee over the loss of a pilot and jet over what they believe to be a hoax.
The films starts with Astrophysicist Ryoichi Shiraishi, his fiancee Hiroko, his sister Etsuko, and his friend Joji Atsumi witnessing a festival at a local village near Mount Fuji. Shiraishi then tells Atsumi that he has broken off his engagement with Hiroko but gives no reason other than an undisclosed obligation to remain in the village. A mysterious forest fire is then seen near them. Shiraishi rushes out to investigate and disappears during the confusion.