Frederic, who is shy and sensitive, and Hugo, who is heartless and aggressive.  
Frederic is in love with Diana, who is in love with Hugo.  To save Frederic from an unhappy marriage, Hugo tries to distract him by bringing to a ball a beautiful dancer, Isabelle, who masquerades as a mysterious personage and becomes the triumph of the occasion.  
Isabelle is a susceptible maiden in her own right, who not only breaks up all the cynical romances that have been going on before she arrives, but she loses her heart as well.