Tragedy has befallen the Russian submarine, Ussuri. Without explanation, the vessel has been lost to the depths of the ocean, all hands aboard presumed lost. A team of deep-sea divers has been dispatched to investigate. What they will discover is the infinity of depths and landscapes that become only more alien to them. And as the team themselves are stricken by yet another tragedy, they must face the increasing reality of the possibilities that lay below. That what awaits them could be the ultimate truth. Or madness. Or both.