A Frenchman appears in Iwon Gasowski's estate near Vilnius, who desperately wants to buy an indebted estate and a house that is about to collapse. When the owner does not want to sell it, the old door unexpectedly disappears from the house. First one, then the other... Secondary school professor Gasowski, a historian, asks his brightest student, Adam Cisowski, known for his detective skills, for help in solving the mystery of incomprehensible thefts at his brother's house. It turns out that everything is to blame for a letter found in Paris in 1836 by Kamil de Berier, a colonel of the Napoleonic army, who during the retreat from Moscow, just before his death, left clues about the hidden treasure.—G