Custom-painted bulldozer rolls for Romney

An ancient meteorite crashes onto the Earth's surface. Six construction workers later begin work building an airstrip at the site, on an island off the coast of Africa.

Foreman Kelly (Clint Walker) and bulldozer driver Mack (Robert Urich) uncover the meteorite, which emits a strange sound. When the bulldozer (a Caterpillar D9) is used to try to shift the meteorite, it emits a blue light and seems to possess the bulldozer. Mack, standing nearby as this occurs, falls ill and then dies. Chub (Neville Brand), the team's mechanic, can not find anything wrong with the non-functioning bulldozer, but can hear the odd sound behind the scoop. Kelly orders that the bulldozer not be used.

Beltran (James A. Watson Jr.) ignores the prohibition and starts the bulldozer, bringing it to malevolent life. It destroys the camp's only two-way radio and begins a rampage, killing the workers one by one. It seems to run indefinitely in spite of a limited fuel capacity. The machine has some rudimentary intelligence and guile, and hunts down the men.