National Park Service Rangers Kathy West and Nathan Toland are the only ones stationed at Fort Jefferson, a restored Civil War fort sixty miles off Key West, Florida. Two overnight campers go missing, but before the rangers can investigate, shady Homeland Security agent Glen Larsson arrives to close the park due to a purportedly imminent red tide.

Things quickly escalate out of control when mercenaries arrive to back up Larsson and imprison the rangers. Larsson’s plan is to free a cast of giant crabs to overrun the park, and then Florida beyond.

It’s up to Kathy and Nathan to escape the fort, and then, with the help of an old Coast Guard vet and a scientist with inside knowledge of the plot, to save millions of innocents from rampaging giant crabs. But Larsson’s evil plan has been decades in the making, and the crabs seem indestructible. It will take courage, teamwork, and perhaps the ultimate sacrifice, to avert disaster.