An asteroid shower lands in a remote section of the Grand Canyon and begins to spread mysterious pods. Meanwhile, scientists on a space station that has been hit by the same asteroid shower, discover that a pod has mutated into a creature and is threatening the ship. Now the scientists and a team on Earth must learn to defeat this alien force, fighting fire with fire, fighting stone with stone.
Years after an alien invasion nearly extinguished the human race, three soldiers who survived on a secret moon base are sent to Earth to liberate the survivors from the Sentinel and its army and reclaim Earth at any cost.