On a record-breaking test at the 1,300 foot level, David Cracken swam out into the blackness - and disappeared. There was no way for him to get back on his own, if indeed where still alive. Yet something brought him back...
------------------

Under the sea, buried deep in the ocean bed miles down, lie unbelievable deposits of the resources man has come to depend upon. Not only oil, uranium and other fuel sources, but actual treasure - pearls, precious unmined stones and metal elements, gold, silver - a whole untapped world of riches lying in wait for millenia.
There are other things that lie in wait also. And with the invasion by man of this last frontier, the things of the undersea depths united to defend their own.
As with any frontier, there were merchants, traders, miners and others who needed protection. So there was a Sub-Sea Academy - not only for protection, but for exploration of its own. Indeed, the Sub-Sea Fleet spearheaded the high technological research, the building of undersea domes, the development of potential mine-rich areas.
So it was the men of the Sub-Sea Academy who were the first to encounter the inhuman and near human creatures of the deep.