really great criminal—one who commits his crime, and then—does nothing! Even I, Hercule Poirot, might fail to catch such a one.”

But I had not followed his words. A light had burst upon me.

“Poirot! Mrs. Renauld! I see it now. She must be shielding somebody.”

From the quietness with which Poirot received my remark, I could see that the idea had already occurred to him.

“Yes,” he said thoughtfully. “Shielding some one—or screening some one. One of the two.”

I saw very little difference between the two words, but I developed my theme with a good deal of earnestness. Poirot maintained a strictly non-committal attitude, repeating:

“It may be—yes, it may be. But as yet I do not know! There is something very deep underneath all this. You will see. Something very deep.”

Then, as we entered our hotel, he enjoined silence on me with a gesture.