Mars’ Imperial Majesty takes control of Battle Group Seven for the “master invasion” of the Arcturus System, and places “Enforcer Drones” on all spaceships to assure compliance. When one Martian officer objects, a drone incinerates him. Meanwhile on Earth, citizens of Big Bean, Illinois, prepare for Halloween 1988. Townspeople also celebrate the new Interstate off-ramp that will bring in commercial traffic. Newly hired Sheriff Sam Hoxley maintains contact with his deputy, Russell Pilsbury, who sits in a cruiser near the off-ramp with a radar gun and video recorder, ready to arrest Big Bean’s first speeder. On the main street, Sam Hoxley stops “Old Man” Wrenchmuller from threatening Farmers Trust president Steve W. Klembecker with an empty shotgun. Klembecker claims he has the right to foreclose on Mr. Wrenchmuller’s property tomorrow at noon, unless the old farmer can pay his mortgage. Later, Sam comforts his daughter, Kathy Hoxley, who does not like her new town because there is nothing to do. Besides, she misses her late mother. Kathy dresses as a space alien to go “trick-or-treating.” As dusk falls, the local radio station, WELZ, celebrates the fiftieth anniversary of Orson Welles’s infamous 1938 radio presentation of H. G. Wells’s The War of the Worlds by rebroadcasting it. As Big Bean townspeople listen to the dramatization of an invasion from Mars, one of the Martian ships of Battle Group Seven, having lost contract with the fleet, picks up the radio transmission in deep space. Mistaking the radio program for a distress signal, the Martian commander, Captain Bipto, joins what he thinks is an attack on Earth. Meanwhile, Sam Hoxley drives Kathy to a Halloween party at Mrs. Vanderspool’s house. Elsewhere, Farmer Wrenchmuller shares a dog biscuit with his dog, “Jim,” and frets over how he will pay off the loan tomorrow, while Deputy Russell Pilsbury awaits a speeder at the off-ramp. Suddenly, as a spacecraft flies by his patrol car, Deputy Pilsbury is shocked that it registers 3,000 miles an hour on his radar gun. The craft crashes into Wrenchmuller’s barn. Inside the crippled ship, four of the five Martian crewmen—Captain Bipto, Lieutenant Giggywig, Dr. Ziplock, and Corporal Pez—decide to go out and “kick some Earthling butt,” while the pilot, Blaznee, stays behind with the enforcer drone to repair the ship. Seeing the invaders, Mr. Wrenchmuller hurries into his house and consults an old comic book about a Martian attack. The aliens on the magazine cover look exactly like the ones in his barn. The old man decides that saving the earth is up to him. As Captain Bipto ventures across a highway, Steve Klembecker hits him with a pickup truck and keeps driving. When Klembecker stops at a gas station, he tells mechanic Vern Pilsbury to scrape off whatever is on the grill. Vern informs Klembecker that his car will be ready the next day. At Mrs. Vanderspool’s house, Kathy meets Brian Hasket, an African American boy dressed as a duck. Brian is impressed with Kathy’s alien costume, which resembles the creature from the 1979 film Alien. Nearby, Dr. Ziplock, Corp. Pez, and Lt. Giggywig approach, but because of their short stature, the Earthlings think they are other children in costume. Kathy likes the Martians’ cute little robot, Shortstuff, which in turn seems fascinated with her. When Mrs. Vanderspool rounds them all up and drives them into town in her station wagon to begin treat-or-treating, the Martians play along. Elsewhere, Capt. Bipto, having been scraped off Klembecker’s grill with a snow shovel, revives at the gas station and puts a clamp on Vern Pilsbury’s neck that turns him into an android. Unable to contact the fleet, Bipto decides to build a new battleship. Vern offers to build his own invention, the “farm-zoid,” from automobile and tractor parts. Meanwhile, in Mrs. Vanderspool’s station wagon, Lt. Giggywig fires a rocket out the window and makes her angry. When Kathy asks Shortstuff where he is from, the little robot’s head screen displays a photograph of Mars. To dampen Mrs. Vanderspool’s growing concern about the rowdy Martians, Kathy explains that they are her cousins from California, but then whispers to Brian that she suspects they are really from Mars. When Giggywig threatens Mrs. Vanderspool with nuclear annihilation and calls her “Earth scum,” she stops the car and orders the three aliens out of the car. Kathy and Brian also leave the station wagon. Sheriff Sam Hoxley finds Deputy Russell Pilsbury’s empty patrol car with its paint burned off and removes the videocassette from the video recorder. Not far away, the deputy arrives at Wrenchmuller’s barn and tries to arrest Blaznee, but a booby-trapped bale of hay knocks him unconscious. The enforcer drone tells Blaznee he has failed and “zaps” him. Sheriff Sam Hoxley hurries home with the videocassette and watches an image of the Martian space ship fly by the deputy’s car. When Wrenchmuller sneaks into the barn to take a photograph of the unconscious Blaznee, he encounters the awakening, dazed deputy sheriff. They put the Martian in the back of Wrenchmuller’s pickup truck and head for the Veterans of Foreign Wars (VFW) lodge in town, where the SpookLuck Halloween dinner is being held. The enforcer drone searches for the other Martians. Meanwhile, Kathy and Brian trail the three aliens. As Wrenchmuller and Deputy Pilsbury tell everyone at the VFW about the little alien in the back of the truck, Blaznee revives in time to escape before they can look at him. However, Sheriff Sam Hoxley arrives and assures everyone that Wrenchmuller is telling the truth about an alien invasion. The three Martians blow up a television store across the street from the VFW and announce through the display televisions that they have landed and are taking over Earth. Mistaking a grain silo for a missile on a launch pad, they shoot it with a heat ray, causing the grain inside to erupt as hot oatmeal. The townspeople run home to get their guns. Spying on the three aliens, Kathy is confronted by Shortstuff, but the robot befriends her and shows on a map where the Martian ship is located. Brian befriends Blaznee and agrees to help him fix his ship. Ziplock, Pez, and Giggywig go to the radio station to inquire about the on-air invasion, but the radio announcer informs them that the Martians died due to infection by Earth germs. Realizing the broadcast was a hoax, the aliens decide to return to the ship and try to escape. Meanwhile, Blaznee repairs the propulsion system, and as he starts the engine, Wrenchmuller slips onboard and tosses Brian outside. He confronts Blaznee, but the Martian locks him inside a force field. As Blaznee tries to take off, the ship belly-flops on a nearby highway. The other four Martians and the “android-ized” Vern Pilsbury join him. Kathy and Shortstuff head there, too. Several trucks of armed townspeople arrive and start shooting, prompting the Martians to consider blowing up the planet, but Kathy pleads with Shortstuff to stop them. Sheriff Sam Hoxley orders townspeople to cease firing. The Martians, standing inside the doughnut-shaped “Doughnut of Destruction,” command the Earthlings to surrender or be destroyed. However, the doughnut malfunctions and fizzles out. Wrenchmuller is released from his suspended animation. Sam Hoxley takes Kathy, Brian, Wrenchmuller, and Vern Pilsbury back to town and puts Deputy Russell Pilsbury in charge of the space ship. Kathy pleads with her father not to tell the outside world about the Martians, because they are not really bad, just stupid, and he should help them get away. Captain Bipto contacts Vern and orders him to distract the townspeople with his farm-zoid. Kathy and Brian hurry back to the ship in order to help the Martians escape. Wrenchmuller wants to help too, because he has the only photographs of the Martians, and once they are gone, he can sell the pictures for enormous prices and save his farm. Blaznee discovers that the hyperdrive is having a nuclear meltdown, and alerts the others that if they do not return the ship to zero gravity within the hour, the resulting explosion will destroy Earth. Wrenchmuller tells the aliens the solution is in his barn. He takes them there in Klembecker’s car and gives them enough dynamite to blow the ship into space. Vern’s mind is restored, and Sheriff Sam Hoxley agrees to let the Martians leave. Suddenly, the enforcer drone arrives to take control of the aliens, but Wrenchmuller offers it a stick of dynamite as a token of appreciation and blows it up. Igniting the rest of the dynamite, the old farmer blasts the Martian ship high enough into space to prevent nuclear meltdown. In appreciation, the Martians drop clouds of green light over Wrenchmuller’s farm. The next day, when Steve Klembecker comes to foreclose on the property, the fields are full of crops super-fertilized by the green stuff from the ship.