As Halloween approached, Billy (Calem MacDonald) and his friends Dallas (Isaiah Fortune) and Trish (Emma Vickers) decided to take their playful rivalry to a new level by targeting the sprawling estate of Samantha (Phoebe Rex), the older sister of Gary (Dominic Mariche), Jack (Asher Grayson), and Miles (Ben Tector). Tired of the incessant bullying by these self-proclaimed party kings, who seemed to revel in making their lives miserable during the filming of their homemade fantasy project in a rustic barn, Billy's newfound interest in Samantha added extra tension to the scenario. He attempted to win her over with feigned passion for her love of action figures and wrestling, deepening the rivalry. Meanwhile, an accident left Gary with a broken arm while filming a stomach-churning wrestling scene, resulting in a stern reprimand from their parents.
As the days wore on, Billy skillfully persuaded Samantha to host a Halloween party at her parent's grand mansion. However, his true intentions were far from noble. He planned to use the event as the ideal setting for his own gathering, aiming to flaunt his relationship with Samantha and establish his dominance over the neighborhood. Unbeknownst to Samantha, Billy's friends were quickly turning the once-inviting house into a disaster zone, wreaking havoc in their wake.
Fed up with being the underdogs, Gary, Jack, and Miles took control of the situation. They equipped themselves with a drone camera to document the chaos happening below, capturing the unruly behavior of Billy's partygoers. But when their spying was discovered by Billy, he snapped, rallying his friends into a frenzy as he threatened them with violence.
Just when it felt like the night couldn't get any worse, alien creatures—previously seen terrorizing fishermen—invaded the party, scattering guests in a frenzy of panic. Amid the confusion, Gary, Jack, Miles, Billy, Dallas, and Trish became ensnared by the extraterrestrial menace. Luckily, Samantha managed to outsmart the chaos, locking herself in her bedroom, where despair washed over her like falling autumn rain as she witnessed her so-called friends destroy her home.
Seizing a fleeting chance, Samantha donned her scuba gear and dove into the lake, where she also infiltrated the alien spacecraft hidden beneath the water. What she discovered was horrifying: aliens using a strange, gooey substance to dissolve Trish—an unsettling revelation that Gary later speculated was a crucial element for their energy source. Meanwhile, a different slime transformed Dallas into a vicious creature with razor-sharp claws. Armed with a peculiar sword she found, Samantha bravely battled several aliens to rescue her brother from the same fate as Trish. Meanwhile, Billy frantically utilized the scuba suit to make his escape, while Sam cleverly helped herself and the three boys flee the submerged lair by synchronizing their breaths.
Upon their return to the house, they encountered Billy trying to evade Dallas's intense pursuit. As they banded together, Gary and Samantha found a renewed camaraderie, momentarily forgetting their earlier squabbles in unity against their shared danger. They sought refuge in the barn, where their film project had once flourished. In an unexpected twist, Billy took Samantha hostage with the sword she had initially wielded for protection. This prompted the three boys to launch a daring rescue mission. However, during the chaotic clash, Billy fatally stabbed Jack, plunging the sword into his stomach. As Miles tended to Jack’s wounds, Dallas's arrival compelled Billy to escape, leading the siblings to confront their deranged brother.
As the alien ship's tractor beam drew Gary toward it, Miles acted quickly on Jack's last-minute suggestion to ignite their film's fireworks finale. The explosive device was drawn into the sky, resulting in a catastrophic explosion that obliterated the extraterrestrial craft and saved Gary. Despite Jack clinging to life, Samantha, Gary, and Miles rushed to get him to safety, but they were soon surrounded by the remaining aliens. Just when despair seemed imminent, armed soldiers from an unknown organization arrived, swiftly dispatching the creature threat. The soldiers then captured the kids, placing them in stasis as they awaited evacuation by another ship.
In a chilling post-credits scene, an unforeseen alien emerges amidst the ruins of Samantha and Gary's home. Their oblivious parents return, eager to find their children, while an ominous figure lurks in the shadows, targeting Samantha and introducing a new wave of danger with the same slimy substance that had previously mutated Dallas.
