It is 1940. When the feverish evacuation of Allied soldiers continues on the beaches of Dunkirk, the ultramodern Polish submarine ORP "Orzeł" glides beneath the sea. The well-trained crew has had spectacular successes, including a daring escape from Tallinn and the sinking of the German transport ship "Rio De Janeiro". Now she is faced with a mysterious and dangerous mission, during which she will have to face not only the threats of underwater mines, depth charges, enemy ships and patrolling airplanes, but also the increasingly tense atmosphere on board. What will happen in the following days will go down in history and will write the legend of the most famous Polish ship.