In the beautiful underwater reefs off the coast of Florida's pastoral Pajaro Island, a fissure rips open in the ocean floor. When graduate student Greg Chambers encounters the seismic readings, he rushes to tell his professor, Anthony McAlister. Greg suspects that a massive earthquake is about to give the small island a rude awakening. To make matters worse, the epicenter is right under Pajaro Island's new resort, where Anthony's estranged wife Lynn is working. As they drive to warn Lynn, the quake tears through the small town, damaging downtown and leveling several homes. The bridge connecting the island to the mainland is wiped out. Lynn and three others are trapped underground in the resort's utility tunnels. When Greg is killed during a rescue attempt, Lynn is forced to rally the survivors to try and save themselves. With aftershocks tearing through the site, the tunnels growing more and more unstable..