Godzilla (Marc Cerasini Series) - Godzilla at World's End

In the third novel, Godzilla at World's End, a new threat emerges from within the Earth itself a year after Godzilla's battle with King Ghidorah. An ancient civilization, long dead and buried beneath Antarctica, springs to life with the arrival of a teenage girl from the surface world, who becomes corrupted by the power she finds there and seeks to destroy mankind, unleashing five new monsters: Gigan, Megalon, Manda, Battra and Hedorah. Her ultimate weapons are the Babel Wave that cuts off all communications and the plant monster Biollante. With the help of a group of teenage scientists, Mothra, a young Rodan (the one that hatched from the egg on Mount Rushmore), and the newly awakened Anguirus, Godzilla makes it to the city in the earth. During the trip Gigan, Hedorah, and Battra are supposedly killed while Manda and Megalon flee into the wild. Godzilla and Biollante have a final battle with Godzilla winning, saving the earth. However Godzilla becomes trapped in the Earth's center. As the book ends the Russian government shows interest in studying Anguirus while America and Japan work together on a new project. It is then revealed that Manda and Megalon are still at large along with Rodan.