When villages in Mexico are attacked by a strange winged creature,ornithologist and Elsie's old fiance Lawrence Cohen calls H.E.A.T. for help. They quickly discover the beast is Quetzalcoatl, an evolutionary hybrid of bird and dinosaur capable of breathing fire and protected by impenetrable feathers. The team must find a way to stop the creature, but matters worsen when Quetzalcoatl takes Elsie to feed its starving young.

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.