In Rutland, Vermont, a nerdy video store clerk named Melvin J. Weals rants in his basement apartment about how he intends to unleash demons on earth in order to eliminate Andy Smith, the husband-to-be of Helen Back, the woman Melvin desires.
In a distant galaxy, Lila Cheney is performing a rock concert. During a break, her roadie, Guido Carosella (Strong Guy), informs Lila that the sound engineer, Rabo, picked up a subspace transmission indicating Earth is about to be invaded by aliens. He begs her to teleport him home, and she does so, depositing him outside the former X-Factor headquarters in Eagle Ridge, West Virginia. With no one there to help, he unsuccessfully tries to contact Xavier’s School for Gifted Children, but is able to reach the Muir Island Genetic Research Facility. He persuades Rahne Sinclair (Wolfsbane) and Jamie Madrox (Multiple Man), as well as the visiting Hank McCoy (Beast), to meet and aid him in dealing with the impending invasion.
Later, on Halloween night, Melvin drives to the Donnybrook Country Club, where Andy and Helen’s reception is taking place. Also being hosted at the club is a costume party. Melvin sneaks into the building’s basement, where he begins his ritual.
Guido welcomes Rahne, Jamie and Hank, who arrive in Excalibur’s craft, the Midnight Runner. Using scanners aboard the plane, Hank locates a dimensional rift in central Vermont, so the team sets off to investigate. On the way, Guido uses the onboard Shi-ar wardrobe transmogrifier to generate a new uniform.
They arrive at the country club to find the two parties in full swing, while above, a dimensional vortex swirls and grows. To blend in, they use the transmogrifier to create Halloween costumes: Frankenstein’s monster, a vampire, a mummy and a werewolf. With in the club, they find no signs of unusual activity, so Hank returns to the Runner to cobble together an apparatus to monitor the vortex and pinpoint its source.
Soon, Strong Guy finds the basement which has transformed, resembling a hellish cavern. Within, Melvin dons the talisman which will control the demons he intends to unleash, a fiery wig called the Hell Toupee. At that moment, a foul ooze seeps through the walls of the reception hall. Guido strikes Jamie to generate a duplicate, whom he dispatches to get the partygoers to evacuate the building.
Melvin then makes his appearance at the reception, trapping the guests and announcing his intent to feed Andy and the wedding guests to the coming demons. He crows that this will allow him to wed Helen, but she is familiar with Melvin as no more than a video store clerk. Guido frees the partiers and the guests, then confronts Melvin. Outside, Beast has devised an ultra-sonic cannon to reverse the growth of the vortex.
Melvin sees that the guests are gone and, fearing the demons will feed on him instead, rushes to the portal in the basement, hoping to close it. But he trips and the talisman falls from his head. Strong Guy puts on the Toupee and orders the demons to return whence they came. They obey, and Hank’s cannon begins to close the portal. Before it shuts, Strong Guy tosses the talisman through it, sealing it off from earth. Melvin runs away.
The heroes celebrate the averted demonic invasion, and Lila arrives to collect Guido. He says he wants to stay a while to catch up with the rest of his former teammates in X-Factor, but Jamie informs him Alex Summers (Havok) had died. Saddened, he reluctantly returns with Lila.
Back at the light years distant concert hall, Guido tells Rabo to play for him the invasion report Rabo had picked up. Guido recognizes it as Orson Welles’ 1938 radio broadcast of “War of the Worlds”.