Plot:
An English couple, Harry and Evelyn, is on a beach when she disappears. In LA, reporter, Jonathan Clark, is taken. In China, soldiers have just widowed Su Tan who disappears. A professor, Klaus Venker, and a Russian soldier, Ivan, are taken aboard the UFO.

Foolish human, you can't ignore my intimidating entrance forever...
The alien explains how their home planet is going to be destroyed by a natural disaster in 35 days. He will give them each weapons that only work for 27 days and explains how to activate and use them. Their alien code won't let them kill intelligent life but are able to let humans go ahead and eliminate themselves. The weapon will only destroy humans. He returns them to Earth.
Evelyn tosses hers away. Su Tan commits suicide to disable her weapon. Later, Evelyn calls Jonathan who she plans on seeing.
Later, the alien broadcasts to all Earth about the people he gave the weapons to and even names them off, too. Professor Klaus gets accidentally run over by a car. Russians chase Ivan down. Jonathan and Evelyn manage to get into hiding. The US recovers the capsule of the Professor's.
As a Russian general questions Ivan who denies everything, Evelyn and Jonathan hide out at a horse race track.
A news report announces that Evelyn tossed her capsule into the ocean. The Russians can't figure out how to arm Ivan's. They torture him into catatonia.
US agents question Professor Klaus who wheedles around the answers. Meanwhile, Jonathan and Evelyn are getting on each other's nerves.
Some goons try to kidnap the Professor from the hospital. The feds shoot than and are able to save the Professor.
The weight of the situation preys on Jonathan. Apparently, a non-Herbie love bug has bitten the two. He and Evelyn decide to turn themselves in.
The Russians use a truth serum on Ivan. He opens that box and reveals how to arm the weapon, too.
The Professor has an idea about the capsules. He, Jonathan, and Evelyn demonstrate how the capsule can be opened...Russia announces that the US must evacuate their forces from Europe and Asia and to stay in the US. The military decides to test one of the capsules at sea. Professor Venker's friend, Professor Carl Newhouse, subjects himself to a fatal dose of radiation to be used as the guinea pig in the blast radius.
The 27 days is over in a few hours. Professor Venker realizes that the capsules have a message written on the entire set. He examines Jonathan's to attempt to decipher.
Russia plans to use their capsules to destroy North America. Ivan rushes at the General, but some guards shot Ivan.
Professor Venker starts to activate the capsules which cause the Russian general to collapse.
The radio announces that the radiation killed all the enemies of human freedom.
Everyone is thinking about what has happened. Jonathan thinks about allowing the aliens to move to Earth and inhabit deserts, jungles, etc...Later, at the UN, Earth sends a message to the aliens and is awaiting their response when they accept.