In the last months of World War Two, the German Navy premiered a new and terrifying weapon--a submarine of incredible range that could strike anywhere, anytime. It was just what Hitler needed to turn the tide of war until it disappeared without a trace. Now, more that seven decades later, the wreck of a previously unknow U-boat has been found off the South American coast. A team of marine archeologists arrive at the unique seafloor habitat to study the wreck up close, but something has survived on the stricken sub--a dark and terrifying presence. A panicked researcher's distress call, brings John Decker to assess the situation.