Sophie and her friends, Marianne and Delphine, are surprised to win places on a school trip to Russia. But the trip does not go as expected. Abandoned on an express train heading out of St Petersburg, the girls are thrown out at a disused station, where they are rescued and taken to the beautiful but faded Volkonsky Winter Palace, as guests of the exotic Princess Anna Feodorovna Volkonskaya.

Guarded by white wolves, the princess is an enigmatic figure, desperately searching for a rope of lost diamonds that could overturn the Volkonsky bad fortune. At first the girls are mesmerised by her stories but when she takes a special interest in Sophie, they begin to be afraid.