Divers descend into the cold, oxygen-poor waters of the Baltic Sea, where the near-absence of light and salt has preserved wrecks and cargo that would have rotted away almost anywhere else. The film follows expeditions hunting for sunken battleships from past wars alongside stranger finds, including sealed champagne bottles more than a century old that come up still drinkable. Underwater footage shows hulls resting largely intact on the seabed, while divers and researchers work to identify vessels, date cargo, and piece together what happened to ships that vanished decades or centuries ago. The Baltic's unique chemistry becomes a character in its own right, explained through interviews with the people who spend their careers exploring it. Between wreck sites, the film treats each discovery as a small mystery: what a ship was carrying, why it sank, and what its condition says about the water that swallowed it. The result is a tour of one sea's buried history, told through the objects it refused to destroy.