French nuclear tests irradiate an iguana into a giant monster that viciously attacks freighter ships in the Pacific Ocean. A team of experts, including Niko Tatopoulos, conclude that the oversized reptile is the culprit. Before long, the giant lizard is loose in Manhattan as the US military races to destroy the monster before it reproduces and it's spawn takes over the world.

Unlikely heroes must overcome incredible dangers to save mankind from the threat of an alien invasion.

On July 2, a giant alien mothership enters orbit around Earth and deploys several dozen saucer-shaped 'destroyer' spacecraft that quickly lay waste to major cities around the planet. On July 3, the United States conducts a coordinated counterattack that fails. On July 4, a plan is devised to gain access to the interior of the alien mothership in space, in order to plant a nuclear missile.