The Great Patriotic War. During the retreat of parts of the Red Army, there was a transfer of secret weapons - the BM-13 Guards mortars, later called Katyushas. During the operation, one machine sank. To prevent it from falling into the hands of the enemy, a group of several masters of sports under the command of Alexander Ermakov is urgently forming and being thrown behind the front line. Their goal is to find and destroy the gun ...