Hot summer of 1943. Our troops are driving the enemy to the border of the USSR, but the enemy is still strong and is preparing to meet them on its territory, on the fortified bridgeheads of East Prussia. Selected SS units, Wehrmacht reserves and Hitler’s “weapons of retaliation”, which no one has yet seen, are gathered here. State Security Commissioner Sudoplatov and his fighters have a real job - to find out the location of the letter train transporting the secret development of the Nazis and destroy it. And the Soviet reconnaissance and sabotage group, abandoned deep behind enemy lines, has only ten days to do this...