Britt is dictating a letter to Casey while preparing for a night out. He pours a drink and says that he and his date are having a late dinner. As they talk, the radio announces that a UFO has crashed in a field outside the city. Britt calls Kato in as they listen to a report that the UFO exploded, but not before several individuals fled the saucer. Mike calls and reports that there are rumors of invasion, and people are fleeing the city. Suddenly there’s a burst of smoke and silver-clad figures burst in through the balcony. They subdue Kato with a burst of electricity, and then address Britt by name.
The alien leader, Mabouse, explains that they are wayfarers and that the female alien, Varna, subdued Kato with a mild electrical charge. Mabouse tells them that they sought out Britt so they can use his television station to convince the authorities leave the aliens alone. All they want is safe passage to a deserted area so their sister ship can pick them up. If Britt refuses, their ships will destroy the city. Further, Britt’s announcement will calm the panic. Mabouse knows that Britt has a camera in his home, and Britt agrees to make a calming broadcast.
Next, Mabouse tells Britt to call the authorities and have a specific route of town cleared. When he says the authorities will refuse, Mabouse warns that Varna will signal the ships to attack, and Britt has Casey call Scanlon on his private line. Britt tells Scanlon what the aliens want, and Scanlon notes that there is nothing in that area of interest. The publisher is skeptical, but Scanlon is willing to accept the aliens’ story and clears the route. Mabouse and his people depart, taking Casey with them and stunning Britt and Kato unconscious.
The aliens take a car out of town and escort Casey to a semi that is luxuriously appointed on the inside. It also contains advanced electrical equipment. Mabouse removes his alien costume and Casey realizes that they’re masquerading as aliens. When she asks why, Mabouse says that he was a scientist who was too advanced for his time, and now seeks power.
Scanlon arrives at Britt’s apartment and tells Britt and Kato that the Air Force is bringing through a shipment of nuclear warheads. Britt realizes that he recognizes Mabouse as a scientist who blew up a facility years ago while developing weapons against foreign powers. The Green Hornet and Kato head for the highway, realizing that whatever Mabouse’s intentions, he could inadvertently set off a nuclear explosion.
The Air Force convoy starts to receive a broadcast warning them of Mabouse’s plans, but Mabouse jams the signal before they can decipher it. The Green Hornet and Kato pick up the signal, and realize that Mabouse is responsible. In the van, Casey activates a Hornet tracking signal, and the heroes home in on her.
One of Mabouse’s men brings in a device, and Casey slips the transmitter into his pocket. The convoy arrives ten minutes early, and Mabouse tells Casey that in a few minutes, they’re going to bring a nuclear warhead on board. He’ll arm the warhead and drop it. He offers her a glass of champagne and invites her to toast his success. She throws it into the control console and runs outside. The “aliens” give pursuit, unaware that Casey is hiding beneath the semi. Once they’re gone, she steals one of their cars and drives off, and Mabouse’s men give pursuit.
The Green Hornet and Kato realize that the scanner is on the move, and it’s changing direction. Meanwhile, Casey’s tire blows out and she’s forced to abandon the car and duck into a culvert and out the other side. She runs across the desert and comes to a lumberyard. The Black Beauty arrives and Green Hornet has Kato stay with the car while he follows the trail.
In the lumberyard, Casey appeals to an elderly worker for helper. The criminals capture her and fasten her to a belt leading up to the incinerator, and then taken on the Green Hornet as they arrive. While Kato arrives to take on the criminals, the Green Hornet climbs up the belt and frees Casey while the criminals flee.
The Air Force convoy pulls to a halt when they find Varna blocking the road in front of them. She stuns them with her electrical blasts, and Mabouse and his men emerge. One of Mabouse’s men attaches the activator device to the truck, and Mabouse warns the colonel that if he interferes, he’ll set off the bomb.