When unexplained catastrophes strike around the globe, geophysicist Dr. Josh Keyes (Eckhart) and French atomic weapons expert Dr. Sergei Leveque (Karyo) are summoned to Washington, D.C., to determine if covert enemy action is to blame. Working with his team at the University of Illinois, Keyes discovers the mystery behind the tragedies is more frightening than any act of war-the earth’s inner core has stopped rotating. As a result, the planet’s electromagnetic field, which shields the earth from deadly solar radiation, is collapsing. If the problem is not resolved quickly, airplanes will start falling from the sky and everything electronic will be destroyed. Static discharge in the atmosphere will create "super-storms" with hundreds of lightening strikes per square mile, and deadliest of all, microwave radiation will literally cook the planet.

Terrified by his findings, Keyes seeks out of the opinion of renowned geophysicist Dr. Conrad Zimsky (Tucci), an arrogant scientist who arrives at the same horrifying conclusion. Together, they determine that the only way to reactivate the core is to travel to it. Scientist Dr. Ed Brazzleton (Lindo) has developed an untested subterranean craft that they hope will be able to penetrate deep into the earth, as far as the core. Now it is up to Keyes, a team of scientists and astronauts Major Rebecca Childs (Swank) and Commander Robert Iverson (Greenwood), who have just been recruited as the world’s first "terranauts," to drive this high-tech vessel into the earth, detonate a nuclear device and somehow restore balance to the planet.