Svetlana Zakharova, now 26 and a principal dancer with the Bolshoi Ballet, based in Moscow, is a remarkable onstage force. For seven years, Ms. Zakharova was the brilliant young face of the Kirov Ballet, in St. Petersburg, where she spent one year in the corps before being promoted to principal dancer; in 2003, she surprised the dance world by defecting to the Bolshoi.”