Five Red Army soldiers, who found themselves in the rear of the Kolchak troops, captured an enemy armored car and captured an intelligence officer. From him they learn that soon a steamer with weapons and ammunition for the upcoming white counteroffensive is due to pass along the river. How to stop the ship, capture it, and then transport such a valuable cargo through ambushes and cordons of Kolchak troops entrenched on both sides of the river?..