Off the coast of Italy, at 120 meters, divers find a German U-boat standing almost vertically on the seafloor, its hull swallowed by sediment. Marine archaeologist Lorenzo del Veneziano leads the investigation into U-455, an intact wreck that raises an immediate question: how did it end up here, and what happened to its crew? The film follows the dive team as they document the hull, work through wartime naval records, and piece together the submarine's final patrol in the Mediterranean. Interviews with historians and archaeologists sit alongside underwater footage of the wreck itself, corroded metal and open hatches standing in for a crew that never surfaced. The investigation moves between the physical evidence on the seabed and the paper trail of Kriegsmarine deployments, weighing rival explanations for the sinking against what divers can actually see on the hull. It is as much a procedural about underwater archaeology as it is a war story, tracking how a single wreck gets identified and how its last hours get reconstructed decades later.