Since the film's release, it has been widely praised both for its above-average storyline and its farsighted portrayal of the consequences of over-consumption of both natural and man-made resources; it has achieved minor cult status as a result.
A huge, blinking flying saucer from deep space emits a glowing object, which races to Earth. It intercepts a man who's driving his car down an isolated road. The object takes over the man's body and directs it to LabCentral, a U.S. research facility that's been tracking the saucer, thinking it was an asteroid.
The man's possessed body forces its way into the lab and the entity inside takes control of the chief scientist, who directs three nuclear missiles to be fired at the saucer. Everyone is shocked when the explosion fails to destroy the object. The saucer crashes into the Pacific Ocean off the coast of Mexico. Impatient with the delay in getting a formal expedition to the crash scene, two of the lab's scientists (one with his photographer girlfriend in tow) head down to Mexico. After their arrival, they see the saucer appear on the ocean's surface. Terrified, they flee back to their lodging for the rest of the night.
The next morning, both scientists and the girlfriend see a large, stories-tall machine that has appeared on the beach. Its four-legged body features two mobile antennae that resemble the terminals of a capacitor. They use a small helicopter to land atop the strange machine, glimpsing its inner workings before being forced to leave the huge machine
Under the direction of the possessed lab scientist, who now has lists of power stations and atom-bomb arsenals around the world, the large machine, which has since been named Kronos, methodically attacks power plants in Mexico, draining their energy entirely. In doing so Kronos grows larger with every energy-absorption episode, consuming more and more power as it moves, unhindered, from one power source to the next. Four Mexican Air Force fighter planes attack Kronos, but the growing alien machine easily destroys them and continues on its energy-draining rampage.
In a lucid, unpossessed moment, the scientist tells his returned colleagues that Kronos is an energy accumulator, sent by an alien race that has exhausted its own natural resources; they have sent their giant machine to drain all the Earth's available power and then return it to their dying world.
The United States Air Force uses a B-47 bomber to drop an atomic bomb, but Kronos draws the jet to crash into it, absorbing the bomb's nuclear blast. The alien machine now grown to an immense size, appears unstoppable, harvesting all forms of energy at will.
As Kronos draws near Los Angeles, scientists devise an ingenious plan that reverses the monster machine's polarity, forcing it to feed upon itself, until being obliterated by a gigantic implosion. But the question remains: Will mankind suffer another onslaught by the desperate aliens?
Kronos was filmed in a little more than two weeks (mid-January to late January 1957) in California; special effects were created by Jack Rabin, Irving Block, and Louis DeWitt. The idea of an alien machine absorbing energy is similar to the giant alien machine from the later (1966) Star Trek television episode "The Doomsday Machine" which destroys planets and uses them to fuel itself.
George O'Hanlon, who plays Dr. Arnold Culver in the film, was later known as the voice of George Jetson in the popular cartoon series The Jetsons.
When the film was first released in 1957, Variety gave the film a favorable review: "Kronos is a well-made, moderate budget science-fictioner which boasts quality special effects that would do credit to a much higher-budgeted film ... John Emery is convincing as the lab head forced by the outer-space intelligence to direct the monster. Barbara Lawrence is in strictly for distaff interest, but pretty".
Film critic Dennis Schwartz was disappointed in the film's screenplay and acting. He wrote, "German emigre to Hollywood, Kurt Neumann (Tarzan and the Amazons/Son of Ali Baba/She Devil), directs this b/w shot, dull, so-so sci-fi film, that's played straight-forward, is humorless and all the thespians are wooden. It's based on the story by Irving Block and the weak script is written by Lawrence Louis Goldman".