Something fishy is going on! The Pyrockians, those fiery little invaders from outer space, are back and they're planning something seriously strange. And what exactly are they doing with an undersea volcano? Would you believe they're evolving into diamonds? It is up to the little merman, young prince Gillbert, to figure out what those pesky Pyrockians are really up to -- but he's gone, with his best bud, Sherbert, to a strange mysterious place in the ocean, called Phiblothian, to meet with Anne Phibean and her pham -- oops, family! Gillbert meets the Phibian Phather, Phinius, Phibster, Phinny, Phil, Phylu, Phibling, Philbert, Phred, Phernando, and the rest.