1658 The Duchy of Courland on the eve of the invasion of the Swedish army. Baron von Neuland decides to bury his treasure. Accidentally sheltering the wandering artist Knage, he orders a painting that should become the key to the treasure for his daughter if the baron dies. Neyland's nephew, guessing the meaning of the painting, orders Knage a copy. And so does the baron’s niece. Nowadays, all three paintings appear almost simultaneously in the Riga antiquarian salon, the collection of a businessman and the Polish provincial museum. A bloody hunt immediately begins for them. Someone, clearly well aware of the secret of the cipher, seeks to cut off possible competitors and take possession of the treasures!..