Dr.StevenSorensonplanstotapthegeothermalenergyoftheEarth'sinteriorbymeansofathermonucleardevicedetonateddeepwithintheEarth.DespitedirewarningsbyfellowscientistTedRampian,DrSorensonproceedswiththeexperimentaftersecretlylearningthatheisterminallyill.Thisexperimentcausesacracktoformandgrowwithintheearth'scrust,whichthreatenstosplittheearthintwoifitisnotstoppedintime.