The last months of the Great Patriotic War are underway. A group of special forces sailors under the command of Senior Lieutenant Balandin receives a secret order of particular importance - to penetrate the enemy's rear and destroy gun mounts on a submerged tanker and German seaplanes on the lake in order to ensure the free landing of Soviet troops. A detachment of nine communist volunteers was given a day to carry out the order, there is no intelligence, the sabotage group can only rely on its own forces, take everything upon itself.