As the first Shark Wars series arc draws to a close, hero Gray unexpectedly finds himself the ruler of the ocean. He's got to make wise decisions in a time of upheaval and isn't sure if he's up to the task!

Dangerous prehistores are loose in the Big Blue, and Gray must defeat their evil leader, Grimkahn. But if he is to do that, he and Barkley must first outsmart the sneaky and dangerous frilled shark, Hokuu. . . .