Tony and his dance partner/wife Gaby headline a Paris musical. Tony becomes the unwilling target for the attentions of performer Yvette. She is later murdered with the dagger used by Tony and his wife in their act, and Gaby is accused of the crime.
“Professor Calthrop, actuated only by scientific motives, and his assistant, out for his own gain, have invented a system for the manufacture of diamonds.” - BFI.