Sub-Atlantica is an undersea kingdom in "the deepest part of the Atlantic", populated by telepathic, human-sized mermen. Its origins are unknown, and in spite of — or perhaps because of — its very high technology, the humans seem unaware of its existence outside of the traditional Atlantis myth. Its ambitious king, Nergill, seeks to conquer the surface world, but all of his technology is powered by geothermal vents, and leaving them would render his weapons useless. However, when a partnership with the Decepticons gives him energon-cube technology, his goals are at last within reach.