The Deep by Nick Cutter

A strange plague called the ‘Gets is decimating humanity on a global scale. It causes people to forget—small things at first, like where they left their keys, then the not-so-small things, like how to drive or the letters of the alphabet. Their bodies forget how to function involuntarily. There is no cure.

But far below the surface of the Pacific Ocean, a universal healer hailed as “ambrosia” has been discovered. In order to study this phenomenon, a special research lab has been built eight miles under the sea’s surface. But when the station goes incommunicado, a brave few descend through the lightless fathoms in hopes of unraveling the mysteries lurking at those crushing depths…and perhaps to encounter an evil blacker than anything one could possibly imagine.