A small town gradually becomes aware of a strange creature which picks off people one by one. But what is this creature, and where is it? At the same time, a seismologist is working in the area, she detects _tremors_. The creature lives underground, and can 'pop up' without warning. Trapped in their town, the town-folk have no escape.

When an army of Graboids - giant, carnivorous underground worms - threaten the Petromaya oil refinery in Mexico, its owners call on Earl Bassett, who once helped kill four of the creatures in Perfection, Nevada. Having squandered the money that came from his resulting celebrity status, Earl is convinced by the $50,000-a-head bounty offered, as well as the enthusiasm of admirer Grady Hoover, who becomes his partner. At Petromaya, Earl and Grady meet geologist Kate Reilly, and begin Graboid hunting, tricking several Graboids into swallowing bomb-rigged, remote-controlled cars. When they find they're facing a lot more Graboids than they ever expected, Earl calls his friend Burt Gummer, a survivalist who arrives well-stocked with weapons.

Third Tremors movie takes us back to the small Nevada town of Perfection where local resident and adventurer Burt Grummer returns after traveling abroad and killing carnivorous worms called "Graboids" (introduced in the first movie) and their offspring "Shriekers" (introduced in the second movie) to life in his home town and must deal with some crooked land developers, a thrill-seeking guy named Jack Sawyer looking for wealth in this potential tourist town, and eventually dealing with a new strain of Graboid worms that meta-morph into their second Shrieker phase, and whom unexpectedly morph into their third stage for another harrowing battle against Burt and Jack in the desert surrounding the town.

In 1889, the site that will become Perfection Valley is home to the town of Rejection Valley. The inhabitants are completely dependent on a nearby silver mine for its income, and when a hot spring causes graboid eggs to hatch the mine becomes too dangerous to work in. Its owner is Hiram Gummer, great-grandfather of Burt. He arrives in town to fix the problem, but finds he is in way over his head dealing with the monsters. As Hiram picks up the lessons that will one day be imparted to Burt, the town readies itself for a final showdown with the graboids.

The giant, man-eating Graboids are back and even deadlier than before, terrorizing the inhabitants of a South African wildlife reserve as they attack from below-and above.