As the mournful notes of the cello brought the four minutes of The Dying Swan to a close at The Hague on January 24, 1931, the audience was in tears. Throughout the performance, there had been no dancer — only a moving spotlight emphasizing the absence of Anna Pavlova, the ballerina the world loved. She had died the day before, of a mysterious lung infection that began almost immediately after her train had left Paris. She'd told doctors she suspected she'd been poisoned. Unable to reach a diagnosis, they treated her symptoms but failed to save her. For Soviet émigrés...