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?"
"In its leaden case in the big safe—the safe purposely appears to be of an old and worn-out pattern, but it is really a triumph of the safe-maker's art. That is probably why the thieves were unable to open it."
"How long are you keeping this radium in your possession?"
"Only for two days more, monsieur. Then my experiments will be concluded."
Poirot's eyes brightened.
"And Inez Veroneau is aware of the fact? Good—then our friends will come back. Not a word of me to any one, madame. But rest assured, I will save your radium for you. You have a key of the door leading from the laboratory to the garden?"