Genetically engineered to live in the sea, Nere Hanson and her friends face daunting new challenges as they race to find a solution to climate change. Nere must begin training for a dangerous new mission: diving deep into the black, cold Twilight Zone to salvage a research ship that sank in mysterious circumstances the day Dai Kuron's mother died. This salvage mission becomes even more perilous when the Sea Rangers spot shredders and a silver sub lurking outside of Safety Harbor. Nere and her team may have to face Whitey, Wasp and Ran Kuron once again, but whose side is Dai Kuron really on? Nere and her dolphins must also make a difficult journey south to find Cam Cruz, her best friend from childhood, and ask for his help. But Cam is a different person now, hardened by his time spent in a Western Collective prison camp. He's even become a member of the most ruthless smuggling gang in the Southern Sector. Can Nere and her Neptune companions make new allies and navigate an ocean of threats including the Marine Guard, cutthroat smugglers and relentless rebels on the prowl? In this action-packed conclusion to The Neptune Trilogy, Nere must decide whom to trust and whom to love.