Nancy meets Helene and Henri Fontaine, refugees from Centrovia who own a dancing school in River Heights. Strange circumstances have brought the brother and sister to the United States.
When they receive an anonymous note threatening their lives, Nancy offers to help.
Encountering numerous puzzles during her investigation, Nancy wonders if the Fontaines are involved with the Centrovian underground. Are they being threatened by their own countrymen?
Is a series of paintings by Henri Fontaine being used for a sinister purpose?
What is the significance of the scarlet ballet slippers that had once belonged to their mother?
The girl detective faces grave danger while looking for answers to these intriguing and intricate questions.