XVIII century. Courland. The corpse of a young girl was discovered on the estate of Karl von Hackeln, near Mitau. At the same time, von Hackeln’s niece, Erica, appears on the estate. She asks her uncle to help her urgently get to the Russian capital. In addition, von Hackeln's old acquaintance, Mikhail Nechaev, suddenly bursts into the house. He is looking for a certain crazy girl who was kidnapped at birth from a noble St. Petersburg lady. The whereabouts of the girl were recently discovered at a great cost, and the lady demands that her daughter be brought to her place. Realizing that the crazy woman is the same drowned woman and that those looking for her do not know her face, von Hackeln invites Erica to pretend to be a “fool”, get to St. Petersburg and decide her own affairs there. However, His Majesty Chance had his own way!..