Anton Tobias is your typical slacker teenager, indulging in a laid-back lifestyle with two supportive parents and close friends, Pnub and Mick. His crush on the girl across the street, Molly, seems like the only excitement in his otherwise mundane life. This tranquility is shattered when a series of gruesome murders strikes their town, and tragedy hits Anton's home when his parents are brutally killed on Halloween night. Suddenly, all signs point to Anton as the main suspect.
In a shocking turn of events, Anton finds himself accidentally killing Mick with a bottle and accidentally decapitating Pnub with a circular saw blade. These horrific acts lead Anton to discover that his right hand is possessed, with sinister intentions tied to the darkness of Hell. His hand's first act of mischief is to toss his cat across the street after a tussle for the remote control. Confused yet determined, Anton finds himself ringing Molly's doorbell, leading to an unexpected romance.
Amidst his personal chaos, he holds a makeshift funeral for his deceased parents and his friends. However, Pnub and Mick refuse to ascend to Heaven, claiming the distance is "too far." Instead, they resurrect in their former bodies, albeit a bit worse for wear—Mick still sporting a bottle in his head and Pnub being decapitated. Together, this unholy trio must confront Anton's treacherous hand.
Meanwhile, a high priestess named Debi LeCure, played by Vivica A. Fox, has uncovered a pattern in the murders nationwide, connecting them into a pentagram shape. This knowledge adds urgency to Anton's plight, especially after his possessed hand claims two of his old high school classmates. In a desperate move, Anton cuts off his own hand with a cleaver, and with Mick's help, they try to stop it once and for all.
Amidst their chaotic misadventures, the trio attempts to retrieve Anton's runaway hand, culminating in a wild chase that includes stealing Randy's truck and accidentally knocking out Debi. As a couple making out in a car meets an untimely end, Anton desperately seeks to warn everyone, but his pleas are met with ridicule. The situation grows even more dire at the Halloween dance where the hand wreaks havoc, killing the lead singer Dexter Holland of The Offspring and sending the crowd into a frenzy.
Molly and her friend Tanya find themselves trapped in the chaos, ultimately leading to Tanya's tragic end. In a frantic effort to save Molly, Anton and his friends confront the hand one last time. Armed with a herbal remedy for inspiration, they manage to weaken the hand enough for Debi to deliver the final blow with a ritual dagger—though it comes with unintended consequences for Mick.
In a bittersweet resolution, Anton ends up in the hospital with Molly at his side, having chosen love over the afterlife. Mick and Pnub, now angelic figures watching over him, share some levity as they adjust to their new roles. As the eerie message "I'M UNDER THE BED" glows from above, Anton is left to ponder his fate amidst the comedic chaos of his new reality.
