“Yes, I have no doubt that it was upon her information that they acted. But what is this precious thing that the thieves failed to find? Jewels?”

Madame Olivier shook her head with a faint smile.

“Something much more precious than that, monsieur.” She looked round her, then bent forward, lowering her voice. “Radium, monsieur.”

“Radium?”

“Yes, monsieur. I am now at the crux of my experiments. I possess a small portion of radium myself⁠—more has been lent to me for the process I am at work upon. Small though the actual quantity is, it comprises a large amount of the world’s stock and represents a value of millions of francs.”

“And where is it?”