The world above has lost contact with the Hollow Earth Special Forces. With the clock ticking down to an even greater earthquake, and one that could spell the end of all life on the surface or our planet, the world leaders decide to try again, but this time using the entrance found in Mount Shasta.

A team of specialists and volunteers join a military expedition to discover what truly caused the Big One that killed billions of people around the planet and destroyed most of the major cities.

While the new team is being readied to start its mission, the old team is still lost beneath the Earth, wondering if they will ever reach their goal or return home safely.