When Gwen Ericksen's infant daughter is kidnapped by the insidious Nereus Project, she and her battle-hardened team embark on a perilous mission to rescue the child. But first, they must locate the elusive Nereus III, the mobile deep-sea station believed to be the project's beating black heart.

All of the team have fought monsters before, from giant mutated isopods to massive anglerfish-piranha hybrids, but nothing in their past can possibly prepare them for what they must now confront...in the Dark Abyss.