The beginning of a tetralogy about the adventures of Princess Sofia Astakhova. The Astakhov princes are not rich, and for this reason, daughter Sophia is not married at 25 years old, and son Nikolai, an officer of the Life Guards, has neither money nor connections. However, thanks to Sonya's adventurous character and courage, curiosity and perseverance, the Astakhovs will get out of poverty and learn the secret of the death of their alchemist grandfather. After the death of her mother, Sonya secretly leaves St. Petersburg for France to find untold riches belonging to her grandfather Eremey Astakhov and his friend the Marquis de Barras. Sonya is ready for the tests of fate, but it happens that the Queen of France Marie Antoinette herself entrusts her with a secret assignment. Poor Sonya didn’t think then about why she was offered the role of a courier. At that moment, Sonya simply took her breath away from the bright prospect of visiting the Austrian court! Suspicions will come later, but, alas!.. the course of events will already be inevitable...