Cover-up rogues imperil Laura and Rich, who are dogged by assassins while seeking evidence of the predatory sea creatures. Also: Niles goes to great lengths to protect Nim, whose discovery has serious ramifications with Niles' parents.

Laura, Rich and Jackson try to use the submersible device they built to investigate the spawning site. But when Rich and Laura begin to descend, they experience technical difficulties that endanger their lives. Elsewhere, Miles does volunteer work at an aquarium.