One hundred miles off the coast of Puerto Rico, a top secret experiment too dangerous to be conducted on land is being conducted aboard the U.S. nuclear attack submarine Sam Houston—an experiment that has gone horribly wrong. A predator is loose in the Sam Houston—a microscopic killer that strikes without warning, driving its victims to terrifying heights of violent, self-destructive insanity. Soon madness and terror reign eight hundred feet below the ocean's surface, as those infected race to defeat the silent killer—unaware that another enemy follows in their wake. A diesel submarine relic is pursuing nuclear-powered Sam Houston into a final, deadly confrontation in the deepest waters of the Atlantic.