A shadowy extraterrestrial emissary summons English woman Eve Wingate, Los Angeles reporter Jonathan Clark, German scientist Professor Klaus Bechner, Chinese villager Su Tan and Russian soldier Ivan Godofsky onto a flying saucer. Once aloft, the alien explains to his incredulous passengers that he has come from a nearby planet on the verge of extinction. The aliens have chosen Earth as their new world, but because their moral code forbids violence, the aliens have chosen to give the power of life or death to the five humans assembled aboard the space craft, thus placing the possibility of destruction in their hands. The five are then presented with a case containing three capsules, each capsule capable of emitting lethal radiation that will kill all human life within a 3,000 mile radius. The alien then states that only the capsules’ recipients can trigger them, and that they will be deactivated in twenty-seven days. The alien also discloses that if the five can keep the peace for that time span, the Earth will be spared. The five are then sent back to Earth with their weapons and Eve immediately casts hers into the sea. Su Tan, observing her village in flames from an enemy attack, promptly commits suicide, thus de-activating her capsules. Jonathan returns to his newspaper office, and soon after, Eve phones from England to inform him that she is on her way to California. The professor, meanwhile, flies to California to address a conference. To increase the chance of havoc, the aliens interrupt a national television broadcast to describe the lethal capsules and announce the names of their five recipients, thus touching off a nationwide panic. After meeting Eve at the airport, Jonathan goes into hiding with her at an abandoned race track. The professor, startled by the broadcast, steps off a curb and is run down by a car. As the professor lies unconscious in his hospital bed, the U.S. government sends for Dr. Karl Neuhaus, a prominent atomic scientist, to examine the weapon. The Russian military, meanwhile, seizes Ivan’s capsules, but Ivan, desperate to preserve peace, refuses to divulge any information about them. As waves of panic wash across the Earth, Jonathan rails against human nature. While the Russians try to torture Ivan into submission, the U.S. confiscates the professor’s capsules. One day, Jonathan learns that a man resembling him has been killed by an angry crowd. Feeling responsible for the man’s death, Jonathan and Eve decide to surrender to the authorities. Their torture having failed, the Russians administer a truth serum to Ivan, forcing him to reveal the secrets of the capsules. As word spreads that the Soviets have discovered how to activate the capsules, the U.S. government prods Jonathan, Eve and the professor to share the information with them. With only twelve days remaining, the professor uses his mental projection to open the case, and Dr. Neuhaus then suggests testing the efficacy of one of the capsules on a single man at sea. When the Soviets issue an ultimatum that the U.S. withdraw its troops from all foreign soil or face extinction, the government approves a test of the capsules. After dosing himself with lethal radiation, thus insuring certain death, Dr. Neuhaus volunteers to be the test subject. When Neuhaus disintegrates after the capsule is launched, the U.S. pulls its troops home from around the world. As the twenty-seventh day arrives, however, there are still fears that the Soviets will launch their capsules at the last moment, thus wiping out the free world. With just five hours remaining, the professor realizes that the capsules contain a mathematical code and asks Jonathan for his set. As the professor attempts to decipher the code, the Soviets plan their attack. Coming to the realization that the capsules can bring life as well as death, the professor pre-empts the Russian attack by launching his capsules against the enemies of freedom. With evil destroyed, mankind unites in peace and harmony and invites the aliens to live in the uninhabited parts of the Earth. Pleased that the Earthlings have finally overcome their warlike tendencies, the aliens accept.