Adventurer Burt Gummer, Michael Gross, returns to his Nevada hometown of Perfection after tracking Shriekers in El Chaco, Argentina. The town’s protective equipment against Graboids has fallen into disrepair, a consequence of neglect by Miguel [Tony Genaro], Nancy Sterngood [Charlotte Stewart], and her daughter Mindy Sterngood [Ariana Richards]. Walter Chang’s market has been taken over by his niece Jodi [Susan Chuang], and a new resident, Desert Jack Sawyer, [Shawn Christian], arrives with tour groups that turn danger into a show. During one afternoon on a Jack-toured outing, Buford [Billy Rieck] is eaten by a live Graboid, sending Mindy and the others scrambling to warn the town that three Graboids now stalk the area. Burt determines there are three Graboids in the vicinity and stakes out a plan to deal with the threat.
Government agents Charlie Rusk [John Pappas] and Frank Statler [Tom Everett], along with paleontologist Dr. Andrew Merliss [Barry Livingston], arrive and insist that Graboids are an endangered species, blocking the town from taking immediate action. Jack negotiates a tense deal: if they can capture one live Graboid, Burt and the residents will be allowed to kill the remaining two. Meanwhile, Melvin Plugg [Robert Jayne], a fellow survivor from the original attacks, presses Burt to sell his land for development, but Burt refuses, determined to protect what’s left of Perfection.
A Graboid attacks and swallows Burt whole, forcing Jack to improvise. He lures the monster to Burt’s house and uses the underground concrete barriers to trap it, then frees Burt with a chainsaw in a brutal but ultimately successful rescue. Later, Merliss explains that he and the agents were ambushed by Shriekers that emerged from the Graboid they were chasing, and he dies. The group is then trapped on rocks for the night by an albino Graboid—El Blanco, meaning “The White One”—that stalks them.
Miguel deduces that El Blanco cannot produce Shriekers because it is infertile, while Shriekers molt into winged creatures capable of rocket-propelled flight. The new winged forms—later dubbed <i>Ass-Blasters</i>—are deadly, and Miguel is killed by one as it crashes into a metal fence, killing itself. Burt realizes that chemicals in the Ass-Blasters’ stomachs enable their flight, and they suspect these creatures may be able to spread Graboid eggs through their flying ability. Jodi dubs the new form <i>Ass-Blasters</i>.
In town, Nancy and Mindy are ambushed by an Ass-Blaster and retreat to a freezer, where they manage to distract the creature with food. The group, using a mattress as cover from the Ass-Blasters’ infrared vision, reaches Burt’s house but must flee when another creature tries to break in. To stop the proliferation, Burt rigs his house and a stash of MREs to explode, learning that the Ass-Blasters do not multiply but fall asleep after feeding—though they are still dangerous in numbers. The survivors retreat to a junkyard and fashion a potato gun from everyday scraps to ignite the combustible contents inside the Ass-Blasters’ stomachs. They manage to kill four of the winged threats.
Burt is then pinned down by El Blanco, but Jack seizes the opportunity, taking the ultrasonIc watch and affixing it to the final Ass-Blaster. El Blanco swallows the watch, saving Burt and Jodi’s lives in the process. In the aftermath, Nancy manages to secure a captured Ass-Blaster for sale, while Jack begins a romantic relationship with Jodi, much to Mindy’s disappointment. Melvin tries again to press Burt to sell the land, but Burt explains that El Blanco is an endangered species and hunting it is illegal; the town agrees to live in harmony with the creature, transforming Perfection into a federally protected Graboid reserve and sealing Melvin’s hopes of development. Burt finally leaves Melvin standing on a rock as El Blanco circles below, marking a fragile peace between humans and the mysterious guardian of Perfection.
