As tension threatens to break the H.E.A.T. team up for good, major problems arise: a giant bat is terrorizing the countryside of Nigeria, the U.S. military have dredged the Leviathan ship from the bottom of the Pacific, and worst of all, the aliens are back, with an army of monsters under their control and plans to conquer the Earth.

From their secret base on Isle Del Diablo, the aliens assemble their forces. H.E.A.T. desperately fights to resist, but are easily defeated. Once captured and brought to the aliens, they are told that the monster army — including a brainwashed Godzilla — will be used to attack major cities across the world in preparation for a full-scale invasion of Earth. At its head marches the aliens' ultimate weapon: Cyber-Godzilla.

As the aliens and their monster allies attack Earth, H.E.A.T. escapes captivity. They battle to defeat the alien onslaught and free the monsters from their control to help humanity fight back and save the planet from conquest.