Alex Gilman is an author intrigued by the rumor of a Nazi submarine lost--and never found--in the Amazon river. When Alex, his wife, and photographer best friend find the sunken U-boat with the help of a local voodoo woman, it's everything he's hoped for: a story that will make him world-famous. But he doesn't expect what happens afterwards. First, the crew begins to catch glimpses of something darting about underwater--something large and potentially dangerous. Then, at the worst possible moment, the creature decides to confront Alex. What happens next will change him forever. As Alex fights against the changes he starts to notice in his body, he comes to realize: he must confront the inhabitants of Merwitch Lagoon.