The more marine biologist Corrie Duval learns about the mysteries of the open ocean and the illusive creatures that inhabit it, the more questions she has. Where are these creatures coming from, how are they related, and just what is Zeballos Artino hiding? Zeb wishes he could answer Corrie's questions, but there is so much he can't say, and even more that he doesn't know himself. The shadowy figure of the woman in the water plagues him with riddles he can't decipher, and his late father's notebook provides only frustrating clues. ​ But when Zeb discovers someone else is attracting these mysterious creatures with the same sonar device installed on his own boat, he and Corrie must race to uncover the truth before this secret world is exposed and exploited.