Truman McClusky has led the underwater colonies in their fight against the world's superpowers. Climate change has devastated the surface; nations suffer famine, drought, rebellion, rising waters, and apocalyptic coastal flooding. But now, as Mac leads the underwater colonies to freedom and independence, he's faced with the gravest threat of his life: a Russian assassin, hellbent on killing Mac and everyone he cares for. Now Mac must uncover the identity of the killer, face him in combat, and at the same time lead people in battle against the largest underwater force ever assembled.

It's Mac's final test and to win the war he must use every tool at his disposal, including the most surprising and devastating underwater weapons ever invented. If Mac fails, all hope is lost for the future of human colonization on the ocean floors. But the assassin could be anyone ...