 But before his experiments reach a conclusion, a frantic mother begs him to try his untested treatment on her son (Dickie Moore), who has been bitten by a rabid dog.Risking imprisonment or even execution, Pasteur decides he must try to save the child.During the attempt, a Dr. Zaranoff (Akim Tamiroff) arrives from Russia with a group of peasants who have been exposed to rabies, and who have volunteered to receive Pasteur's treatment.