Count Olgierd Łabiński lives in Paris with his beloved wife, but their quiet life is disturbed by the arrival of Octavius de Saville, a former admirer of the Countess from her days in Florence. Obsessed with possessing her, Octavius seeks out Dr. Cherbonneau, a sinister figure dabbling in Eastern teachings of reincarnation. Through the doctor’s occult science, Octavius attempts a dangerous “exchange of souls,” scheming to inhabit the Count’s body and win the woman he desires.

During the Napoleonic wars, a Spanish officer and an opposing officer find a book written by the former's grandfather.