Hans Kloss (Tomasz Kot) - a Polish intelligence agent code-named J-23 - finds a treasure stolen by the Nazis. Kloss's old friend Hermann Brunner (Piotr Adamczyk) is involved in the plot. Kloss, trying to thwart the enemy's plans, tries to save the beautiful Elza (Marta Żmuda Trzebiatowska) from the conflagration of war, for whom he will be ready to risk the safety of his mission.